Like Dicer said, work it gently with a heat gun. Go slow and clamp the edges when you get it where you need it (use wood/heavy cardboard shims under the clamps so you don't distort the vinyl). When it's mostly back where you want it, GENTLY (plastic putty knife) separate the vinyl from the backer board. Use your old backers as templates and cut some new ones out of 1/8" masonite. If the padding self-destructed when you removed the vinyl, replace it- I use that thin sheet foam like they use for packing sometimes...Use contact cement to reattach foam to new backers, when that dries reattach the vinyl to the foam- use lots of spring clamps/shims. Note: you MUST have some kind of padding between the vinyl and the backer board, or you will never be able to insert the panel clips so you can install your newly reconditioned door cards...!
