Saving a document or form as a PDF file can be done in a number of ways: most of Adobes applications can save or export to PDF directly. If you're on Mac OS X, you always have the option to "save as PDF". There are also third-party solutions, for instance the free Express PDF that will let you create a PDF from any web page, Word documents or Excel spreadsheet.
Here's how to do it on your own, provided you have Acrobat Distiller installed:
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Actually, this is one of the rare occasions in life when there IS a "best way" of doing things:
With your form opened in your favorite application:
You should now have a PostScript file named "my_form.ps" (probably located in the same folder as the original file) containing your form.
TIP: If you don't own a PostScript printer, pretend that you do:
Close your eyes and try to imagine the new and shiny color A3 state-of-the-art PostScript laser printer on the desk right beside your monitor, angry and full of carbon. Now install it:
Control Panel->Printers->Add printer->Local Printer->Create a New Port->Local Port->enter "my PDF port"->Browse for a PostScript printer driver (I chose Canon ColorPass Z5000) and voila! You just got a virtual PostScript printer virtually attached to your computer, ready for use from virtually any program!