This patent stuff is scary...

If patent holders can restrict you from doing some stuff with their products, does it mean that if you hold a patent on something that a user creates, you can limit what that user can do with those?

I'm thinking of something along those lines:

• A file format, or a portion of a file format gets patented
• You buy a software that creates such files

Does it mean the software maker can say, for example, that you can't use a third-party tool on the files you create? That would be very scary.