Is weatherstripping a DIY project?

You should be able to do it yourself. Ask the hardware store or DIY shop for instructions.

This is certainly a DIY project. I review the door weatherstripping every fall and replace as needed or when drafts or light is seen.
There are a variety of products, so outside the installation part is what product to select.
The differences will vary based on how the door and the jam currently fit to. Feel free to reach out if you have specific questions one you look at the door.
A couple of links to review:
DIY Network
Garage door
ehow

It’s very easy. The weather stripping comes in long rolls with an peel off adhesive back.

All you need to to is cut to length, peel off the protective paper over the adhesive, and stick it into place.

It’s so easy even I can do it, and I have.

Yes, you can do it yourself. This comes from a guy who makes a living as a handyman. The house doors probably are the stick on variety or the weatherstripping is in a “kerf” or groove in the door frame. Just remember that in the winter everything shrinks in the cold and a real tight fit now will stick in the summer. The garage doors frequently have a rubber gasket attached to a backer of wood or PVC trim. A flat prybar will remove the trim and sometimes it can just be moved closer to the door. Sometimes moving this piece exposes an area that will need to be painted. Everything shrinks in the winter, a tight fit in the cold will stick or the door will hang up on it this summer. While you’re at it, add insulation behind the cover plates on all exterior walls. Hardware stores sell a flat sheet that is designed for this, it already has the holes in the right place. Just remove the cover, put the sheet over the switch or outlet(carefully) and screw the plate back on.

If you have steel doors replacing the w/s will be a snap. When you pull out the old w/s you will see what to do. Usually scissors is all you need to cut the new w/s to the right length. If your doors are wood chances are you may have to use what’s called “jamb up” w/s. Again the old w/s will clue you what to do assuming it’ still there. You might need tin cutters to cut the pieces to length and a screw driver to fasten the pieces to the door frame, or a cordless drill is a much better tool for that.