I have a PDF file with other PDF files attached to it. Acrobat shows them in "Attachments" tab and allows to open them in turn.
QPDF documentations says something about extracting attachments but I failed to find any particular commands that do that.
Is it possible to extract these attachments and have them stored on the disk as separate PDF files?
UPDATE: Just a notice to explain better what you can see in the UI: "Attachments" tab was present in older versions of Acrobat, as well as a special page of the container document recommending to download newer version of Acrobat (this page seems to be really existing as it is shown in other viewers as well as on preview image). Latest versions of Acrobat (Reader) skip this page and get you to the first attached document, with the list of all attachments shown on the left side of the screen.
I found an old GitHub issue which a little bit clarify the possibilities of attachment extraction.
It is possible to extract attachments from PDF files using the qpdf
library by understanding the PDF file structure and pulling the
attachments out "manually" by knowing which objects to extract. There
is nothing in the public API at the moment nor in the command-line
tool that enables you to work with attachments as a first-class thing,
but there is an item in the TODO list, and there is some private code
used internally to detect cases where attachments are encrypted
differently from the rest of the file. The main reason, aside from
lack of time, that attachments are not more directly supported is
because there have been various ways that they are stored in the file,
and I don't know whether I have examples of all of them. I'm reluctant
to add a feature for attachments that may miss some attachments in
some older PDF files.
https://github.com/qpdf/qpdf/issues/24
So, it seems it is possible but you should examine the details of the pdf file.
Starting with qpdf 10.2, you can work with file attachments in PDF files from the command line. The following options are available:
http://qpdf.sourceforge.net/files/qpdf-manual.html#ref.attachments
Given a PDF file. Can I find out which software/libraries (e.g. PDFBox, Adobe Acrobat, iText...) where used to created/edit it?
The Adobe specification defines the Producer field (see 'Mac OS X 10.5.6 Quartz PDFContext' in screenshot nimeshjm's answer) as the name of the application that "converted from another format to PDF". In case of generating a PDF programmatically, the PDF isn't really converted so you will normally find the name of the generating SDK here.
The Creator field is related and is defined as the name of the application that created the document from which the PDF was converted. This is typically MS Word or so.
Note that this is all by convention. In practice, you cannot really rely on this and you may encounter for example empty Producer fields.
You can try opening the file in Adobe Acrobat Reader and look at the properties.
You can find this in: File -> Properties in Adobe Acrobat Reader after you open the pdf file.
You can probably get away without any PDF libraries for this type of operation. It won't be 100% reliable but I think you can probably assume 99% reliability.
So... write some code to open your PDF as a text stream and seaarch down for /Producer. You will find something like this:
69 0 obj
<<
/Creator (PDF+Forms 2.0)
/CreationDate (D:20010627111809)
/Title (Demo)
/Producer (Cardiff Software - TELEform 7.0)
/ModDate (D:20010627111810-05'00')
>>
Grab the bits between the parentheses and Bob's your uncle. Technically the text can be stored in other formats to but I think those will be pretty uncommon for this particular type of entry.
If you can't find anything here then look for the XMP data which is always guaranteed to be in clear text. It will look something like this,
39 0 obj
<</Subtype/XML/Length 15172/Type/Metadata>>stream
<?xpacket begin='' id='W5M0MpCehiHzreSzNTczkc9d'?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 4.0-c320 44.293068, Sun Jul 08 2007 18:10:11">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about=""
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:xap="http://ns.adobe.com/xap/1.0/"
xmlns:xapGImg="http://ns.adobe.com/xap/1.0/g/img/"
xmlns:xapMM="http://ns.adobe.com/xap/1.0/mm/"
xmlns:pdf="http://ns.adobe.com/pdf/1.3/"
dc:format="application/pdf"
xap:CreatorTool="Adobe Illustrator CS2"
xap:CreateDate="2006-05-04T15:53:27-07:00"
xap:ModifyDate="2006-05-04T15:53:27-07:00"
xap:MetadataDate="2006-05-04T15:53:27-07:00"
xapMM:DocumentID="uuid:61AC83CBC0DBDA11A32BC847EF128E34"
xapMM:InstanceID="uuid:cba15bf3-d7da-4a4e-a563-fc20d13e258a"
pdf:Producer="Adobe PDF library 7.77">
<dc:title>
<rdf:Alt>
<rdf:li xml:lang="x-default">3.01 PDF components</rdf:li>
</rdf:Alt>
</dc:title>
...
The combination of these two is going to be practically always right. If you want 100% reliablity then by all means use a PDF library but for many purposes this should be sufficient.
My replies may feature concepts based around ABCpdf. It's what I work on. It's what I know. :-)
It is usually difficult to determine which software actually designed a PDF because most of Microsoft Office product can convert an edited file to PDF. By this I mean, opening a regular typed document, you have the option to save it as PDF. If you are familiar with Powerpoint slides, it can be easy to tell based on the design once the file is in PDF.
Where as on the other hand, Adobe Acrobat has the ability to create the file like those application forms we often download (from an embassy site, immigration site, etc).
Other software such as Adobe Photoshop, Illustrator, etc... can save files as PDF. Hope this help.
I'm doing some work with OCRing PDFs, and I'm curious if there is a way to check if a PDF has been exported from Word (or Google Docs). I can check if the PDF has been OCR'd with Xpdf's pdffonts. I know Word and Google Docs automatically OCR the exported PDFs, so if I find that the PDF hasn't been OCR'd. I know it hasn't been exported. But if it has been OCR'd, is there any way to check if the PDF was exported from Word/Google Docs VS simply OCRd with a program like Tesseract? Specifically I'm working in JavaScript but any information is useful.
For anyone looking this up, what I am doing now is using pdfinfo (from Xpdf) with the -meta flag to check if the PDF has XMP metadata. PDFs exported from Word and Google Docs do not have this metadata, but other PDFs do.
We are looking to embed metadata attached to elements as well as individual page objects in PDF but are not clear on whether XMP would be the right solution. As an alternative we have considered embeddeding code in the annotations attached to each object in the pdf.
Any ideas on how to embed metadata to individual pdf elements?
PDF Reference states that:
In general, a PDF stream or dictionary can have metadata attached to
it as long as the stream or dictionary represents an actual
information resource, as opposed to serving as an implementation
artifact. Some PDF constructs are considered implementational, and
hence cannot have associated metadata.
So you might add XMP metadata to almost any stream or dictionary in a PDF file. And to PDF file as whole, of course (i.e to document catalog dictionary).
You will probably need to use a PDF library that is capable to add XMP metadata to document and individual objects within it. Or a library that gives you low level access to PDF objects.
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For a small project I have to parse pdf files and take a specific part of them (a simple chain of characters). I'd like to use python to do this and I've found several libraries that are capable of doing what I want in some ways.
But now after a few researches, I'm wondering what is the real structure of a pdf file, does anyone know if there is a spec or some explanations anywhere online? I've found a link on adobe but it seems that it's a dead link :(
Here is a link to Adobe's reference material
http://www.adobe.com/devnet/pdf/pdf_reference.html
You should know though that PDF is only about presentation, not structure. Parsing will not come easy.
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.
When I first started working with PDF, I found the PDF reference very hard to navigate.
It might help you to know that the overview of the file structure is found in syntax, and what Adobe call the document structure is the object structure and not the file structure. That is also found in Syntax. The description of operators is hidden away in Appendix A - very useful for understanding what is happening in content streams. If you ever have the pain of working with colour spaces you will find that hidden in Graphics! Hopefully these pointers will help you find things more quickly than I did.
If you are using windows, pdftron CosEdit allows you to browse the object structure to understand it. There is a free demo available that allows you to examine the file but not save it.
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.
I'm trying to do pretty much the same thing. The PDF reference is a very difficult document to read. This tutorial is a better start I think.
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.
If You want to parse PDF using Python please have a look at PDFMINER. This is the best library to parse PDF files till date.
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/
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.
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.
You need the PDF Reference manual to start reading about the details and structure of PDF files. I suggest to start with version 1.7.
On windows I used a free tool PDF Analyzer to see the internal structure of PDF files.
This will help in your understanding when reading the reference manual.
(I'm affiliated with PDF Analyzer, no intention to promote)
To extract text from a PDF, try this on Linux, BSD, etc. machine or use Cygwin if on Windows:
pdfinfo -layout some_pdf_file.pdf
A plain text file named some_pdf_file.txt is created. The simpler the PDF file layout, the more straightforward the .txt file output will be.
Hexadecimal characters are frequently present in the .txt file output and will look strange in text editors. These hexadecimal characters usually represent curly single and double quotes, bullet points, hyphens, etc. in the PDF.
To see the context where the hexadecimal characters appear, run this grep command, and keep the original PDF handy to see what character the codes represent in the PDF:
grep -a --color=always "\\\\[0-9][0-9][0-9]" some_pdf_file.txt
This will provide a unique list of the different octal codes in the document:
grep -ao "\\\\[0-9][0-9][0-9]" some_pdf_file.txt|sort|uniq
To convert these hexadecimal characters to ASCII equivalents, a combination of grep, sed, and bc can be used, I'll post the procedure to do that soon.