We add a prefix to a word to make a solid word unless there is already a word with that spelling and a different meaning. This occurs most often with the prefix "re-."
...She promises to work to reform her bad behavior.
...After the merger that occurred, we had to re-form the company.
...I have decided to resign from the board.
...We returned to the bank to re-sign the papers.
A couple of interesting examples along these same lines:
...The books on the shelf seem to just multiply over the months.
...It was a multi-ply board.
...The people unionized in an effort to improve working conditions.
...It was an un-ionized compound.
Happy punctuating!
Margie