I have a PDF reader but you can't fill anything in with it. I would have to buy the Acrobat Suite. So someone wanting me to fill out their PDF had better be willing to go buy that for me
But our insurance company did similar: there was the online form you could fill out, but if you wanted to print and snail to us, there was an HTML form, which you could either fill out on the computer and then print, or just print. A print stylesheet turned inputs into
width: something in mm;
border: solid #000;
border-width: 0 0 1px 0;
and we added explanatory text to the print stylesheet (use black or blue pen etc) and removed the submit button and other web-form styling to make it look like our paper forms.
For print this worked fine, except in Firefox because that browser has untold retarded Netscape bugs in it... not being able to print half a fieldset on a single page being one of them. If you have long fieldsets, tell users to use a better, modern browser like IE instead of Firefox