The PDF::Reader library implements a PDF parser conforming as much as possible to the PDF specification from Adobe.

It provides programmatic access to the contents of a PDF file with a high degree of flexibility.

The PDF 1.7 specification is a weighty document and not all aspects are currently supported. We welcome submission of PDF files that exhibit unsupported aspects of the spec to assist with improving out support.

Installation

The recommended installation method is via Rubygems.

  gem install pdf-reader

Usage

PDF::Reader is designed with a callback-style architecture. The basic concept is to build a receiver class and pass that into PDF::Reader along with the PDF to process.

As PDF::Reader walks the file and encounters various objects (pages, text, images, shapes, etc) it will call methods on the receiver class. What those methods do is entirely up to you - save the text, extract images, count pages, read metadata, whatever.

For a full list of the supported callback methods and a description of when they will be called, refer to PDF::Reader::Content. See the code examples below for a way to print a list of all the callbacks generated by a file to STDOUT.

Text Encoding

Internally, text can be stored inside a PDF in various encodings, including zingbats, win-1252, mac roman and a form of Unicode. To avoid confusion, all text will be converted to UTF-8 before it is passed back from PDF::Reader.

Exceptions

There are two key exceptions that you will need to watch out for when processing a PDF file:

MalformedPDFError - The PDF appears to be corrupt in some way. If you believe the file should be valid, or that a corrupt file didn’t raise an exception, please forward a copy of the file to the maintainers and we can attempt improve the code.

UnsupportedFeatureError - The PDF uses a feature that PDF::Reader doesn’t currently support. Again, we welcome submissions of PDF files that exhibit these features to help us with future code improvements.

MalformedPDFError has some subclasses if you want to detect finer grained issues. If you don’t, ‘rescue MalformedPDFError’ will catch all the subclassed errors as well.

Any other exceptions should be considered bugs in either PDF::Reader (please report it!) or your receiver (please don’t report it!).

Maintainers

• Peter Jones <mailto:pjones@pmade.com>
• James Healy <mailto:jimmy@deefa.com>

Mailing List

Any questions or feedback should be sent to the PDF::Reader google group.

http://groups.google.com/group/pdf-reader

Examples

The easiest way to explain how this works in practice is to show some examples.

Naïve Page Counter

A simple app to count the number of pages in a PDF File.

  require 'rubygems'
  require 'pdf/reader'

  class PageReceiver
    attr_accessor :counter

    def initialize
      @counter = 0
    end

    # Called when page parsing ends
    def end_page
      @counter += 1
    end
  end

  receiver = PageReceiver.new
  pdf = PDF::Reader.file("somefile.pdf", receiver)
  puts "#{receiver.counter} pages"

List all callbacks generated by a single PDF

WARNING: this will generate a lot of output, so you probably want to pipe it through less or to a text file.

  require 'rubygems'
  require 'pdf/reader'

  receiver = PDF::Reader::RegisterReceiver.new
  pdf = PDF::Reader.file("somefile.pdf", receiver)
  receiver.callbacks.each do |cb|
    puts cb
  end

Extract all text from a single PDF

  class PageTextReceiver
    attr_accessor :content

    def initialize
      @content = []
    end

    # Called when page parsing starts
    def begin_page(arg = nil)
      @content << ""
    end

    # record text that is drawn on the page
    def show_text(string, *params)
      @content.last << string.strip
    end

    # there's a few text callbacks, so make sure we process them all
    alias :super_show_text :show_text
    alias :move_to_next_line_and_show_text :show_text
    alias :set_spacing_next_line_show_text :show_text

    # this final text callback takes slightly different arguments
    def show_text_with_positioning(*params)
      params = params.first
      params.each { |str| show_text(str) if str.kind_of?(String)}
    end
  end

  receiver = PageTextReceiver.new
  pdf = PDF::Reader.file("somefile.pdf", receiver)
  puts receiver.content.inspect

Extract metadata only

  require 'rubygems'
  require 'pdf/reader'

  class MetaDataReceiver
    attr_accessor :regular
    attr_accessor :xml

    def metadata(data)
      @regular = data
    end

    def metadata_xml(data)
      @xml = data
    end
  end

  receiver = MetaDataReceiver.new
  pdf = PDF::Reader.file(ARGV.shift, receiver, :pages => false, :metadata => true)
  puts receiver.regular.inspect
  puts receiver.xml.inspect

Improved Page Counter

A simple app to display the number of pages in a PDF File.

  require 'rubygems'
  require 'pdf/reader'

  class PageReceiver
    attr_accessor :pages

    # Called when page parsing ends
    def page_count(arg)
      @pages = arg
    end
  end

  receiver = PageReceiver.new
  pdf = PDF::Reader.file("somefile.pdf", receiver, :pages => false)
  puts "#{receiver.pages} pages"

Basic RSpec of a generated PDF

  require 'rubygems'
  require 'pdf/reader'
  require 'pdf/writer'
  require 'spec'

  class PageTextReceiver
    attr_accessor :content

    def initialize
      @content = []
    end

    # Called when page parsing starts
    def begin_page(arg = nil)
      @content << ""
    end

    def show_text(string, *params)
      @content.last << string.strip
    end

    # there's a few text callbacks, so make sure we process them all
    alias :super_show_text :show_text
    alias :move_to_next_line_and_show_text :show_text
    alias :set_spacing_next_line_show_text :show_text

    def show_text_with_positioning(*params)
      params = params.first
      params.each { |str| show_text(str) if str.kind_of?(String)}
    end
  end

  context "My generated PDF" do
    specify "should have the correct text on 2 pages" do

      # generate our PDF
      pdf = PDF::Writer.new
      pdf.text "Chunky", :font_size => 32, :justification => :center
      pdf.start_new_page
      pdf.text "Bacon", :font_size => 32, :justification => :center
      pdf.save_as("chunkybacon.pdf")

      # process the PDF
      receiver = PageTextReceiver.new
      PDF::Reader.file("chunkybacon.pdf", receiver)

      # confirm the text appears on the correct pages
      receiver.content.size.should eql(2)
      receiver.content[0].should eql("Chunky")
      receiver.content[1].should eql("Bacon")
    end
  end

Known Limitations

The order of the callbacks is unpredicable, and is dependent on the internal layout of the file, not the order objects are displayed to the user. As a consequence of this it is highly unlikely that text will be completely in order.

Occasionally some text cannot be extracted properly due to the way it has been stored, or the use of invalid bytes. In these cases PDF::Reader will output a little UTF-8 friendly box to indicate an unrecognisable character.

Resources

• PDF::Reader Code Repository: http://github.com/yob/pdf-reader
• PDF::Reader Rubyforge Page: http://rubyforge.org/projects/pdf-reader/
• PDF Specification: http://www.adobe.com/devnet/pdf/pdf_reference.html
• PDF Tutorial Slide Presentations: http://home.comcast.net/~jk05/presentations/PDFTutorials.html