How do you protect window sills and door frames from scratches?

Brainstorming here:

When my children were learning to walk we put foam pipe insulation over sharp edges in the house. Perhaps that would work for window sills as well.

An old towel folded several times and held in place by the closed window may also help.

Could you cut a piece of plexiglass (or have it cut for you at the store) and used double-sided tape to attach it to the bottom portion of your doors?

Good luck!

My front window is a popular spot for dogs to look outside, and while most of the bigger dogs can look out without hopping up there, mid-small dogs always put their paws up. So far no scratches, so it may be a difference in paints? I'd also try cupboard liner as a cheap, easily replaceable cover.

I'm not sure how big your place is or how big your furniture is, but usually the easiest thing to do and least expensive thing to do is just to move your furniture away from the window. We had a sofa against the living room window and the dog would scratch it up. We got rid of one of the sofa's that was beat up anyways and moved the other sofa across the room and now we don't have the dog scratching up the windows with her nose to the window. And guess what? She can still look out the window from the other sofa across the room and she still loves it!