It's fairly easy to produce something as PDF these days. As others have already mentioned both OpenOffice/LibreOffice and recent MS Office versions will do it natively, as will lots of other programs, and you can also use "Print to File/Print to PDF" drivers for programs that don't do PDF natively.
Editing existing PDFs is a lot tougher, but I've had good luck sometimes just importing the PDF into the GIMP open source graphic editor to change one page. PDF is a publishing format, basically, it's not really designed to be edited once it's been saved in PDF.
For doing stat cards, player handouts and other things that involve graphics, I'm a huge fan of Inkscape -
www.inkscape.org - which is an open source vector graphic editing program. It's got fantastic documentation and tutorials available to get you started, and it's awesomely powerful. I use it all the time to create gaming material.
The "inkscape" tag over on my blog will show you some of what I've used the program for:
http://www.warbard.ca/tag/inkscape/