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Exposing PDF Special Capabilities

PDF provides a number of features to make electronic document viewing more efficient and comfortable, and our library exposes a number of these.

Forms

The Form feature lets you create a block of graphics and text once near the start of a PDF file, and then simply refer to it on subsequent pages. If you are dealing with a run of 5000 repetitive business forms - for example, one-page invoices or payslips - you only need to store the backdrop once and simply draw the changing text on each page. Used correctly, forms can dramatically cut file size and production time, and apparently even speed things up on the printer.

Forms do not need to refer to a whole page; anything which might be repeated often should be placed in a form. The example below shows the basic sequence used. A real program would probably define the forms up front and refer to them from another location.

eg(examples.testforms)

PDF supports internal hyperlinks. There is a very wide range of link types, destination types and events which can be triggered by a click. At the moment we just support the basic ability to jump from one part of a document to another, and to control the zoom level of the window after the jump. The bookmarkPage method defines a destination that is the endpoint of a jump.eg

canvas.bookmarkPage(name,
                    fit="Fit",
                    left=None,
                    top=None,
                    bottom=None,
                    right=None,
                    zoom=None
                    )

By default the bookmarkPage method defines the page itself as the destination. After jumping to an endpoint defined by bookmarkPage, the PDF browser will display the whole page, scaling it to fit the screen:

canvas.bookmarkPage(name)

The bookmarkPage method can be instructed to display the page in a number of different ways by providing a fit parameter. eg:

fit Parameters Required Meaning
Fit None Entire page fits in window (the default)
FitH top Top coord at top of window
FitV left Left coord at left of window
FitR left bottom right top Scale window to fit the specified rectangle
XYZ left top zoom Fine grained control. If you omit a parameter\nthe PDF browser interprets it as "leave as is"

Required attributes for different fit types

Note : fit settings are case-sensitive so fit="FIT" is invalid

Sometimes you want the destination of a jump to be some part of a page. The FitR fit allows you to identify a particular rectangle, scaling the area to fit the entire page.

To set the display to a particular x and y coordinate of the page and to control the zoom directly use fit="XYZ".

canvas.bookmarkPage('my_bookmark',fit="XYZ",left=0,top=200)

This destination is at the leftmost of the page with the top of the screen at position 200. Because zoom was not set the zoom remains at whatever the user had it set to.

canvas.bookmarkPage('my_bookmark',fit="XYZ",left=0,top=200,zoom=2)

This time zoom is set to expand the page 2X its normal size.

Note : Both XYZ and FitR fit types require that their positional parameters (top, bottom, left, right) be specified in terms of the default user space. They ignore any geometric transform in effect in the canvas graphic state.

Note: Two previous bookmark methods are supported but deprecated now that bookmarkPage is so general. These are bookmarkHorizontalAbsolute and bookmarkHorizontal.

canvas.linkAbsolute(contents, destinationname, Rect=None, addtopage=1, name=None, 
thickness=0, color=None, dashArray=None, **kw)

The linkAbsolute method defines a starting point for a jump. When the user is browsing the generated document using a dynamic viewer (such as Acrobat Reader) when the mouse is clicked when the pointer is within the rectangle specified by Rect the viewer will jump to the endpoint associated with destinationname. As in the case with bookmarkHorizontalAbsolute the rectangle Rect must be specified in terms of the default user space. The contents parameter specifies a chunk of text which displays in the viewer if the user left-clicks on the region.

The rectangle Rect must be specified in terms of a tuple (x1,y1,x2,y2) identifying the lower left and upper right points of the rectangle in default user space.

For example the code

canvas.bookmarkPage("Meaning_of_life")

defines a location as the whole of the current page with the identifier Meaning_of_life. To create a rectangular link to it while drawing a possibly different page, we would use this code:

canvas.linkAbsolute("Find the Meaning of Life", "Meaning_of_life",
                 (inch, inch, 6*inch, 2*inch))

By default during interactive viewing a rectangle appears around the link. Use the keyword argument Border='[0 0 0]' to suppress the visible rectangle around the during viewing link. For example

canvas.linkAbsolute("Meaning of Life", "Meaning_of_life",
                 (inch, inch, 6*inch, 2*inch), Border='[0 0 0]')

The thickness, color and dashArray arguments may be used alternately to specify a border if no Border argument is specified. If Border is specified it must be either a string representation of a PDF array or a PDFArray (see the pdfdoc module). The color argument (which should be a Color instance) is equivalent to a keyword argument C which should resolve to a PDF color definition (Normally a three entry PDF array).

The canvas.linkRect method is similar in intent to the linkAbsolute method, but has an extra argument relative=1 so is intended to obey the local userspace transformation.

Outline Trees

Acrobat Reader has a navigation page which can hold a document outline; it should normally be visible when you open this guide. We provide some simple methods to add outline entries. Typically, a program to make a document (such as this user guide) will call the method canvas.addOutlineEntry(self, title, key, level=0, closed=None) as it reaches each heading in the document.

title is the caption which will be displayed in the left pane. The key must be a string which is unique within the document and which names a bookmark, as with the hyperlinks. The level is zero - the uppermost level - unless otherwise specified, and it is an error to go down more than one level at a time (for example to follow a level 0 heading by a level 2 heading). Finally, the closed argument specifies whether the node in the outline pane is closed or opened by default.

The snippet below is taken from the document template that formats this user guide. A central processor looks at each paragraph in turn, and makes a new outline entry when a new chapter occurs, taking the chapter heading text as the caption text. The key is obtained from the chapter number (not shown here), so Chapter 2 has the key 'ch2'. The bookmark to which the outline entry points aims at the whole page, but it could as easily have been an individual paragraph.

#abridged code from our document template
if paragraph.style == 'Heading1':
    self.chapter = paragraph.getPlainText()
    key = 'ch%d' % self.chapterNo
    self.canv.bookmarkPage(key)
    self.canv.addOutlineEntry(paragraph.getPlainText(),
                                        key, 0, 0)

Page Transition Effects

canvas.setPageTransition(self, effectname=None, duration=1,
                    direction=0,dimension='H',motion='I')

The setPageTransition method specifies how one page will be replaced with the next. By setting the page transition effect to "dissolve" for example the current page will appear to melt away when it is replaced by the next page during interactive viewing. These effects are useful in spicing up slide presentations, among other places. Please see the reference manual for more detail on how to use this method.

Internal File Annotations

canvas.setAuthor(name)
canvas.setTitle(title)
canvas.setSubject(subj)

These methods have no automatically seen visible effect on the document. They add internal annotations to the document. These annotations can be viewed using the "Document Info" menu item of the browser and they also can be used as a simple standard way of providing basic information about the document to archiving software which need not parse the entire file. To find the annotations view the *.pdf output file using a standard text editor (such as notepad on MS/Windows or vi or emacs on unix) and look for the string /Author in the file contents.

eg(examples.testannotations)

If you want the subject, title, and author to automatically display in the document when viewed and printed you must paint them onto the document like any other text.

illust(examples.annotations, "Setting document internal annotations")

Image

Encryption

About encrypting PDF files

Adobe's PDF standard allows you to do three related things to a PDF file when you encrypt it:

  • Apply password protection to it, so a user must supply a valid password before being able to read it,
  • Encrypt the contents of the file to make it useless until it is decrypted, and
  • Control whether the user can print, copy and paste or modify the document while viewing it.

The PDF security handler allows two different passwords to be specified for a document: - The 'owner' password (aka the 'security password' or 'master password') - The 'user' password (aka the 'open password')

When a user supplies either one of these passwords, the PDF file will be opened, decrypted and displayed on screen.

If the owner password is supplied, then the file is opened with full control - you can do anything to it, including changing the security settings and passwords, or re-encrypting it with a new password.

If the user password was the one that was supplied, you open it up in a more restricted mode. The restrictions were put in place when the file was encrypted, and will either allow or deny the user permission to do the following:

  • Modifying the document's contents
  • Copying text and graphics from the document
  • Adding or modifying text annotations and interactive form fields
  • Printing the document

Note that all password protected PDF files are encrypted, but not all encrypted PDFs are password protected. If a document's user password is an empty string, there will be no prompt for the password when the file is opened. If you only secure a document with the owner password, there will also not be a prompt for the password when you open the file. If the owner and user passwords are set to the same string when encrypting the PDF file, the document will always open with the user access privileges. This means that it is possible to create a file which, for example, is impossible for anyone to print out, even the person who created it.

Owner Password set? User Password set? Result
Y - No password required when opening file. Restrictions apply to everyone.
- Y User password required when opening file. Restrictions apply to everyone.
Y Y A password required when opening file. Restrictions apply only if user password supplied.

When a PDF file is encrypted, encryption is applied to all the strings and streams in the file. This prevents people who don't have the password from simply removing the password from the PDF file to gain access to it - it renders the file useless unless you actually have the password.

PDF's standard encryption methods use the MD5 message digest algorithm (as described in RFC 1321, The MD5 Message-Digest Algorithm) and an encryption algorithm known as RC4. RC4 is a symmetric stream cipher - the same algorithm is used both for encryption and decryption, and the algorithm does not change the length of the data.

How To Use Encryption

Documents can be encrypted by passing an argument to the canvas object.

If the argument is a string object, it is used as the User password to the PDF.

The argument can also be an instance of the class reportlab.lib.pdfencrypt.StandardEncryption, which allows more finegrained control over encryption settings.

The StandardEncryption constructor takes the following arguments:

def __init__(self, userPassword,
    ownerPassword=None,
    canPrint=1,
    canModify=1,
    canCopy=1,
    canAnnotate=1,
    strength=40):

The userPassword and ownerPassword parameters set the relevant password on the encrypted PDF.

The boolean flags canPrint, canModify, canCopy, canAnnotate determine wether a user can perform the corresponding actions on the PDF when only a user password has been supplied.

If the user supplies the owner password while opening the PDF, all actions can be performed regardless of the flags.

Example

To create a document named hello.pdf with a user password of 'rptlab' on which printing is not allowed, use the following code:

from reportlab.pdfgen import canvas
from reportlab.lib import pdfencrypt

enc=pdfencrypt.StandardEncryption("rptlab",canPrint=0)

def hello(c):
    c.drawString(100,100,"Hello World")
c = canvas.Canvas("hello.pdf",encrypt=enc)
hello(c)
c.showPage()
c.save()

Interactive Forms

Overview of Interactive Forms

The PDF standard allows for various kinds of interactive elements, the ReportLab toolkit currently supports only a fraction of the possibilities and should be considered a work in progress. At present we allow choices with checkbox, radio, choice & listbox widgets; text values can be entered with a textfield widget. All the widgets are created by calling methods on the canvas.acroform property.

Example

This shows the basic mechanism of creating an interactive element on the current page. canvas.acroform.checkbox( name='CB0', tooltip='Field CB0', checked=True, x=72,y=72+4*36, buttonStyle='diamond', borderStyle='bevelled', borderWidth=2, borderColor=red, fillColor=green, textColor=blue, forceBorder=True)

alStyle=TableStyle([
        ('SPAN',(0,0),(-1,0)),
        ('FONT',(0,0),(-1,0),'Helvetica-Bold',10,12),
        ('FONT',(0,1),(-1,1),'Helvetica-BoldOblique',8,9.6),
        ('FONT',(0,2),(0,-1),'Helvetica-Bold',7,8.4),
        ('FONT',(1,2),(1,-1),'Helvetica',7,8.4),
        ('FONT',(2,2),(2,-1),'Helvetica-Oblique',7,8.4),
        ('ALIGN',(0,0),(-1,0),'CENTER'),
        ('ALIGN',(1,1),(1,1),'CENTER'),
        ('INNERGRID', (0,0), (-1,-1), 0.25, colors.black),
        ('BOX', (0,0), (-1,-1), 0.25, colors.black),
        ])

NB note that the acroform canvas property is created automatically on demand and that there is only one form allowd in a document.

Checkbox Usage

The canvas.acroform.checkbox method creates a checkbox widget on the current page. The value of the checkbox is either YES or OFF. canvas.acroform.textfield parameters are

Parameter Meaning Default
name the parameter's name None
x the horizontal position on the page (absolute coordinates) 0
y the vertical position on the page (absolute coordinates) 0
size The outline dimensions size x size 20
checked if True the checkbox is initially checked False
buttonStyle the checkbox style (see below) 'check'
shape The outline of the widget (see below) 'square'
fillColor colour to be used to fill the widget None
textColor the colour of the symbol or text None
borderWidth as it says 1
borderColor the widget's border colour None
borderStyle The border style name 'solid'
tooltip The text to display when hovering over the widget None
annotationFlags blank separated string of annotation flags 'print'
fieldFlags Blank separated field flags (see below) 'required'
forceBorder when true a border force a border to be drawn False
relative if true obey the current canvas transform False
dashLen the dashline to be used if the borderStyle=='dashed' 3

Radio Usage

The canvas.acroform.radio method creates a radio widget on the current page. The value of the radio is the value of the radio group's selected value or OFF if none are selected. canvas.acroform.radio parameters,

Parameter Meaning Default
name the radios group (ie parameter) name None
value the radios group name None
x the horizontal position on the page (absolute coordinates) 0
y the vertical position on the page (absolute coordinates) 0
size The outline dimensions size x size 20
selected if True this radio is the selected one in its group False
buttonStyle the checkbox style (see below) check
shape The outline of the widget (see below) square
fillColor colour to be used to fill the widget None
textColor the colour of the symbol or text None
borderWidth as it says 1
borderColor the widgets border colour None
borderStyle The border style name solid
tooltip The text to display when hovering over the widget None
annotationFlags blank separated string of annotation flags print
fieldFlags Blank separated field flags (see below) noToggleToOff required radio
forceBorder when true a border force a border to be drawn False
relative if true obey the current canvas transform False
dashLen the dashline to be used if the borderStyle=='dashed' 3

Listbox Usage

The canvas.acroform.listbox method creates a listbox widget on the current page. The listbox contains a list of options one or more of which (depending on fieldFlags) may be selected. canvas.acroform.listbox parameters

Parameter Meaning Default
name the radios group (ie parameter) name None
options List or tuple of avaiable options
value Singleton or list of strings of selected options
x the horizontal position on the page (absolute coordinates) 0
y the vertical position on the page (absolute coordinates) 0
width The widget width 120
height The widget height 36
fontName The name of the type 1 font to be used Helvetica
fontSize The size of font to be used 12
fillColor colour to be used to fill the widget None
textColor the colour of the symbol or text None
borderWidth as it says 1
borderColor the widgets border colour None
borderStyle The border style name solid
tooltip The text to display when hovering over the widget None
annotationFlags blank separated string of annotation flags print
fieldFlags Blank separated field flags (see below)
forceBorder when true a border force a border to be drawn False
relative if true obey the current canvas transform False
dashLen the dashline to be used if the borderStyle=='dashed' 3

Choice Usage

The canvas.acroform.choice method creates a dropdown widget on the current page. The dropdown contains a list of options one or more of which (depending on fieldFlags) may be selected. If you add edit to the fieldFlags then the result may be edited.canvas.acroform.choice parameters

Parameter Meaning Default
name the radios group (ie parameter) name None
options List or tuple of avaiable options []
value Singleton or list of strings of selected options []
x the horizontal position on the page (absolute coordinates) 0
y the vertical position on the page (absolute coordinates) 0
width The widget width 120
height The widget height 36
fontName The name of the type 1 font to be used Helvetica
fontSize The size of font to be used 12
fillColor colour to be used to fill the widget None
textColor the colour of the symbol or text None
borderWidth as it says 1
borderColor the widgets border colour None
borderStyle The border style name solid
tooltip The text to display when hovering over the widget None
annotationFlags blank separated string of annotation flags print
fieldFlags Blank separated field flags (see below) combo
forceBorder when true a border force a border to be drawn False
relative if true obey the current canvas transform False
dashLen the dashline to be used if the borderStyle=='dashed' 3
maxlen None or maximum length of the widget value None

Textfield Usage

The canvas.acroform.textfield method creates a textfield entry widget on the current page. The textfield may be edited to change tha value of the widget.canvas.acroform.textfield parameters

Parameter Meaning Default
name the radio's group (ie parameter) name None
value Value of the text field ''
maxlen None or maximum length of the widget value 100
x the horizontal position on the page (absolute coordinates) 0
y the vertical position on the page (absolute coordinates) 0
width The widget width 120
height The widget height 36
fontName The name of the type 1 font to be used Helvetica
fontSize The size of font to be used 12
fillColor colour to be used to fill the widget None
textColor the colour of the symbol or text None
borderWidth as it says 1
borderColor the widget's border colour None
borderStyle The border style name solid
tooltip The text to display when hovering over the widget None
annotationFlags blank separated string of annotation flags print
fieldFlags Blank separated field flags (see below)
forceBorder when true a border force a border to be drawn False
relative if true obey the current canvas transform False
dashLen the dashline to be used if the borderStyle=='dashed' 3

Button styles

The button style argument indicates what style of symbol should appear in the button when it is selected. There are several choices, eg check cross circle star diamond note that the document renderer can make some of these symbols wrong for their intended application. Acrobat reader prefers to use its own rendering on top of what the specification says should be shown (especially when the forms hihlighting features are used

Widget shape

The shape argument describes how the outline of the checkbox or radio widget should appear you can use circle square

The renderer may make its own decisions about how the widget should look; so Acrobat Reader prefers circular outlines for radios.

Border style

The borderStyle argument changes the 3D appearance of the widget on the page alternatives are: solid dashed inset bevelled underlined

fieldFlags Argument

The fieldFlags arguments can be an integer or a string containing blank separate tokens the values are shown in the table below. For more information consult the PDF specification.Field Flag Tokens and values,

Token Meaning Value
readOnly The widget is read only 1<<0
required the widget is required 1<<1
noExport dont export the widget value 1<<2
noToggleToOff radios one only must be on 1<<14
radio added by the radio method 1<<15
pushButton if the button is a push button 1<<16
radiosInUnison radios with the same value toggle together 1<<25
multiline for multiline text widget 1<<12
password password textfield 1<<13
fileSelect file selection widget 1<<20
doNotSpellCheck as it says 1<<22
doNotScroll text fields do not scroll 1<<23
comb make a comb style text based on the maxlen value 1<<24
richText if rich text is used 1<<25
combo for choice fields 1<<17
edit if the choice is editable 1<<18
sort if the values should be sorted 1<<19
multiSelect if the choice allows multi-select 1<<21
commitOnSelChange not used by reportlab 1<<26

annotationFlags Argument

PDF widgets are annotations and have annotation properties these are shown in the table below. Annotation Flag Tokens and values,

Token Meaning Value
invisible The widget is not shown 1<<0
hidden The widget is hidden 1<<1
print The widget will print 1<<2
nozoom The annotation will notscale with the rendered page 1<<3
norotate The widget wont rotate with the page 1<<4
noview Dont render the widget 1<<5
readonly Widget cannot be interacted with 1<<6
locked The widget cannot be changed 1<<7
togglenoview Teh widget may be viewed after some events 1<<8
lockedcontents The contents of the widget are fixed 1<<9