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8 December 2009
This is some info that I wrote some time ago on PDF files (Portable Document Format).
PDF (Portable Document Format), is a popular format for distributing files. It can be read using Adobe's Free Acrobat Reader as well as a number of alternative viewers. The reasons for it's popularity is that files can be read by almost anyone (although they may need to download a viewer), and unlike html the formatting looks the same across different machines. This is different from html which can look different depending upon the operating system, the fonts available and the resolution of the screen.
Whilst Adobe provides a free viewer for PDF files, it's not quite so generous when it comes to creating PDF files. The Acrobat software includes a standard edition priced at £245 + VAT and a professional version priced at £395 + VAT. Fortunately there are cheaper solutions.
A few years ago I listed one solution which involved printing to a postscript file and then using Ghostscript(GPL Version) to convert it to a pdf file. This used the GSview GUI front end to make it easier to control ghostscript.
Fortunately it's now easier than that. Many applications now come with the option to export to PDF directly, including the free OpenOffice.org. If you are wanting to convert an office type document then you can open it in OpenOffice and use the export to PDF option. It does not offer the same functionality as the Adobe software, so you should choose the appropriate option based upon your requirements and budget.
A feature of some PDF creation software is the ability to restrict what the user can do with the document. This is typically things like the ability to change the document, whether the document can be printed and if text can be copied and pasted into a different document or application. These are normally restricted using passwords so that anyone can open and view the file, but to perform additional tasks involves entering the password. This feature is not secure. The Adobe products follow the restrictions but other applications may not. Because of that it is only of any use in protecting the document against the casual user.
The document author may have a reason for using that protection, and I do not condone the removal of the password protection for misuse, but there are sometimes occasion where is it useful to be able to update a document with password protection. It may for example be that you've been handed the task of re-editing a internal document from where the original file has been lost and the password forgotten.
If you have a valid reason for removing the password protection it can be achieved as follows: (software available for Linux, Windows and even OS/2).
* Only use this technique with permission of the document owner
Another useful task is being able to merge multiple documents into a single document. This can be achieved using the free (GPL) PDF Toolkit. After extracting the program to a directory (I put it in c:\utilities as I've added that to my path, or on my Mandriva machine it was installed in /usr/bin) you can then run the program from the command prompt.
pdftk file1.pdf file2.pdf file3.pdf cat output combined.pdf
If pdftk is not in your search path then you will need to enter the full path name e.g.
c:\utilities\pdftk
The above command combines file1.pdf, file2.pdf and file3.pdf into a single pdf file combined.pdf. If the files are password protected then this will need to be removed by following the instructions above, or by providing the password when prompted.
