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.
The recommended installation method is via Rubygems.
gem install pdf-reader
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.
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.
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 (preferably via the google group) and we can attempt to 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!).
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James Healy <[email protected]>
Any questions or feedback should be sent to the PDF::Reader google group. It’s better that any answers be available for others instead of hiding in someone’s inbox.
groups.google.com/group/pdf-reader
The easiest way to explain how this works in practice is to show some examples.
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"
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
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
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
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"
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
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.
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PDF::Reader Code Repository: github.com/yob/pdf-reader
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PDF::Reader Rubyforge Page: rubyforge.org/projects/pdf-reader/
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PDF Specification: www.adobe.com/devnet/pdf/pdf_reference.html
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PDF Tutorial Slide Presentations: home.comcast.net/~jk05/presentations/PDFTutorials.html