We are getting so many documents now in PDF, it would be easier just to paste a signature in. To do that we need Adobe Acrobat or one of its clones. There are an amazing number of editors since Adobe allows anyone to create a writer royalty free. “Wikipedia”:http://en.wikipedia.org/wiki/List_of_PDF_software has a big list. (Even Office 2007 with some obscure add on can now write PDF).
* Adobe Acrobat Standard. This seems to be all hat you need. There is a “pro”:http://www.adobe.com/products/acrobat/matrix.html version whcih adds AutoCAD, Visio and Project conversion, digitally signing PDFs, comparing difference and an even more expensive Pro Extended (what a name!) that lets you make PowerPoint slides additions and embed video into Word. It is $99 for the OEM version and $149 for retail. So amazingly expensive for a conversion product.
* “Acrobat.com”:http://acrobat.com. If you just want to do a simple conversion of Word or other documents into PDF, there is a free utility on the web. Only lets you do five conversions per signup though.
* “Freepdfconvert.com”:http://freepdfconvert.com. If you don’t have a Mac, then there are many free pdf converters on the web. Here is the top hit on Google.
* “Primopdf”:http://primopdf.com is the free converter that runs on your Windows machine.
* “NitroPDF”:http://nitropdf.com is a clone of Adobe Acrobat. It is $99 for the Pro and $49 for Express and there is a free thing called PrimoPDF that just creates. Actually on the Mac, you don’t really need that is Apple includes a PDF by printing. We need the Pro version because it allows editing and adding graphics (like signatures).
I’ve used these, there seem to be a host of google:”PDF Edit” around that are more reasonable priced as “TUAW”:http://www.tuaw.com/2007/03/31/feature-review-pdfclerk-vs-pdfpen/
* “PDFLab”:http://lifehacker.com/software/pdf/download-of-the-day-pdflab-154095.php is a freeware program that also reportedly lets you add images but most folks report it “doesn’t”:http://www.macupdate.com/reviews.php?id=15818 work. It also crashed for me on a one page document, so I think it probably hasn’t been updated for the most recent Acrobat file formats.
* “Skimapp”:http://skim-app.sourceforge.net/ is also open source and allows annotations (but now so does OS X Preview). It can add circles, lines, text, but doesn’t seem to allow adding images 
* “PDFpen”:http://smileonmymac.com/PDFpen. Does all the basics. The main issue is that it died on a 300 page document in the review and you can add in graphics for signatures and it’s files are much smaller. The signature plus the file is 168KB vs 1.5MB for PDF Clerk. For $95, you create fillable forms. I don’t really need this but could be useful for things like being a soccer registrar 
On balance, since our PDFs are short, we’ll take PDFPen. Also, they have a deal where for $75, you get 5 licenses, which is pretty good!
* “PDFClerk”:http://www.sintraworks.com/ is $60 and is uglier but you can also place signatures on. It also lets you clip out a section of a PDF document (for creating an attachment to a memo) and handles renumbering. The good news though is that it doesn’t crash on big documents but it does bloat the files. I took a 50K one page PDF and added a 150K image that was the signature and the result is a 1.5MB PDF. Sigh.