Structure of a PDF file? [closed]

Answer 1

I found the GNU Introduction to PDF to be helpful in understanding the structure. It includes an easily readable example PDF file that they describe in complete detail.

Other helpful links:

• PDF Succinctly book is longer and has helpful pictures.
• Introduction to the Insides of PDF is a presentation that isn't as in-depth but gives a quick overview and has lots of pictures.

Answer 2

Here's the raw reference of PDF 1.7, and here's an article describing the structure of a PDF file. If you use Vim, the pdftk plugin is a good way to explore the document in an ever-so-slightly less raw form, and the pdftk utility itself (and its GPL source) is a great way to tease documents apart.

Answer 3

Didier have a tool to parse the PDF:

http://didierstevens.com/files/software/pdf-parser_V0_4_3.zip

or here:

http://blog.didierstevens.com/programs/pdf-tools/ which cataloged several related pdf-analysis tools.

Another tool is here:

http://mshahzadlatif.wordpress.com/2011/09/28/view-pdf-structure-using-adobe-acrobat-or-a-free-tool-called-pdfxplorer/

Answer 4

Extracting text from PDF is a hard problem because PDF has such a layout-oriented structure. You can see the docs and source code of my barely-successful attempt on CPAN (my implementation is in Perl). The PDF data structure is very cool and well designed, but it's easier to write than read.

Answer 5

This may help shed a little light: (from page 11 of PDF32000.book)

PDF syntax is best understood by considering it as four parts, as shown in Figure 1:

• Objects. A PDF document is a data structure composed from a small set of basic types of data objects. Sub-clause 7.2, "Lexical Conventions," describes the character set used to write objects and other syntactic elements. Sub-clause 7.3, "Objects," describes the syntax and essential properties of the objects. Sub-clause 7.3.8, "Stream Objects," provides complete details of the most complex data type, the stream object.

• File structure. The PDF file structure determines how objects are stored in a PDF file, how they are accessed, and how they are updated. This structure is independent of the semantics of the objects. Sub- clause 7.5, "File Structure," describes the file structure. Sub-clause 7.6, "Encryption," describes a file-level mechanism for protecting a document’s contents from unauthorized access.

• Document structure. The PDF document structure specifies how the basic object types are used to represent components of a PDF document: pages, fonts, annotations, and so forth. Sub-clause 7.7, "Document Structure," describes the overall document structure; later clauses address the detailed semantics of the components.

• Content streams. A PDF content stream contains a sequence of instructions describing the appearance of a page or other graphical entity. These instructions, while also represented as objects, are conceptually distinct from the objects that represent the document structure and are described separately. Sub-clause 7.8, "Content Streams and Resources," discusses PDF content streams and their associated resources.

Looks like navigating a PDF file will require a little more than a passing effort.

Answer 6

One way to get some clues is to create a PDF file consisting of a blank page. I have CutePDF Writer on my computer, and made a blank Wordpad document of one page. Printed to a .pdf file, and then opened the .pdf file using Notepad.

Next, use a copy of this file and eliminate lines or blocks of text that might be of interest, then reload in Acrobat Reader. You'd be surprised at how little information is needed to make a working one-page PDF document.

I'm trying to make up a spreadsheet to create a PDF form from code.