There are a number of character sheets I’ve dug up for this game, none are form-fillable however, so it is a case of printing one out and filling it out by hand, or making your own as you go.
The important thing when making your own really is tracking the difference between your rolled stats, your advancements in your stats, and your current stats.
The classic 1e Character sheet is available for free download from Cubicle 7 via RPGnow. This is the version that appears in the main rulebook.
This version of the character sheet is much denser in layout and manages to fit everything on one side of the page. It was the official sheet for the Hogshead edition of WHFRP1e.
This sheet was included in “Apocrypha 2: Charts of Darkness”. It is much darker and more stylish than the classic sheet, but unfortunately not an incredibly high resolution scan.