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>
That said, a VERY basic character sheet can indeed be made by simply using a *.png to PDF form application. The trick lies, however, in what you want to do with that form once you have fields for it. If you only want fields, that process works. But if you want some calculations to process, you'll have to add code (JavaScript for Acrobat Forms) that process in the background. The added code will definitely increase your file size too.
If you're looking to take a JavaScript-reliant PDF form and present it using the web as your medium, rather than a local application, you'll have to keep that JavaScript function in mind. Also, to keep in mind, is that Acrobat has quite a few of it's own methods and properties defined for the JavaScript syntax.
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.