I find Visio to be one of the more common tools. Next most common is word with screenshots and steps laid out, then lastly powerpoint/MSPaint I have seen alot of for capturing images and drawing basic shapes on them to highlight certain things. Honestly when it comes to writing up PDD's a few core concepts to bear in mind, for the most part PDD's should already exist in a company, it is a document symbolizing a series of steps that is already performed by a team day in/out. The best case scenario is you can take this document, highlight any parts which may be troublesome or not informative and use any of these tools to highlight/fill-in the gaps. Worst case you have no previous PDD then the best you can do is create a document clear and salient enough that when a developer reads it they could perform the process flow without having to ask for directions. If you can make that level of detail then you're golden no matter what tool you use.
Some examples to highlight Visio/Word usage, if you capture a screenshot and highlight any data you can reference your flow diagram with a number/pointer to indicate this part is related to this screenshot etc. Useful thing developers will be grateful for.
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Dexter Whelan
Senior Developer/Mentor
SAS
Europe/London
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