Some code being usually more helpful than long writing, let's learn how to play with origami.

PDF terminology

Here we just explain some words you will see/hear when dealing with a PDF file.

  • object: in a PDF file, everything is an object. Open any file, and you will see something like: 
    42 0 obj <<
   ...
>>
    What is between the <<...>> depends on the kind of object.
  • Dictionary: it is the most common kind of object. You can consider it as an associative array, with Key Value pair. For instance, the code below describes a font. 
    42 0 obj
<<
        /Encoding /MacRomanEncoding
        /Subtype /Type1
        /BaseFont /Helvetica
        /Type /Font
        /Name /F1
>>
endobj
    Note the Type key, which is almost always present in a dictionary.
  • stream: it is a dictionary object containing additional data. The example below is a text which will be displayed on a page: 
    5 0 obj
<<
        /Length 101
>>stream
BT
        1 Tr /F1 30 Tf 350 750 Td (base.pdf) Tj
ET
BT
        0 Tr /F1 15 Tf 186 690 Td (Empty test file) Tj
ET
endstream
endobj

Creating a PDF from scratch

Easy ! We start by creating a stream containing the text which will be printed in the file. Then, we put the text into the file, and save it. 

# Create a simple PDF document. 
contents = ContentStream.new
contents.write 'I AM EMPTY', 
  :x => 350, :y => 750, 
  :rendering => PS::Text::Rendering::STROKE, 
  :size => 15
PDF.new.append_page(Page.new.setContents(contents))
pdf.saveas('out.pdf')

Adding a JavaScript to a PDF

Adding a JavaScript is really easy: you read the PDF you want to modify, and add an OpenAction which executes the JavaScript.

pdf = PDF.read( ARGV[0])
jscript = File.open("fooscript.js").read
jsaction = Action::JavaScript.new(
                   Stream.new(jscript, 
                              :Filter => :FlateDecode) )
pdf.onDocumentOpen(jsaction)
pdf.saveas("out.pdf")

The above example is really simple as we should take care before adding the OpenAction in case another one is already there.

Hiding a file into a PDF

One can add attachment to PDF files. We provide the method attach_file to do it: 

pdf = PDF.read( ARGV[0] )
pdf.attach_file(path, :EmbeddedName => ARGV[1])
pdf.saveas("out.pdf")

More to come ...