I maintain a rather intricate fillable PDF form, intended to be used as a Character Sheet for Pathfinder RPG, you can find it over at <a href="http://www.badassbandannastudios.org" rel="nofollow">http://www.badassbandannastudios.org</a>
If you want users to be able to make changes to values of fields for a PDF form which they're submitting, you may want to factor in any code which the PDF form itself utilizes.
On this whole topic though, my suggestion would be to either: A) simply provide a GM reference sheet that scales for each character, or B) have a space designated for a URL. For option A, just have an interface for the GM that scales with the number of PCs and for the Player, only allow them to see the PCs they "own." For option B, it's easy enough these days to get a direct link to a file via dropbox or google drive or other various cloud services.