Printing from HTML+CSS is notoriously unreliable. (Screen display isn't a whole lot better, but there are bigger problems when it goes wrong in printing, such as the edge of the page and page breaks). While it's fine for general text and information, anything where the layout is really important (which it often is for a form) may be better done as a PDF, especially if it is going to fill most of the page and so not leave you much margin for error.
If you've got a static form and you're going to offer it as a PDF, you might as well take the time to create it from scratch in Word or similar, so that you have it absolutely right and optimised for print. In the grand scheme of things it won't take long at all, and the benefits of having a properly designed printable page are significant.