Some software makers put a limit on using their sharewares which were given for free trial (Giving for free trial DOESNOT make it a freeware, but a shareware) by many methods....
1. Time limit of using (14 days, 1 month etc.)
2. Number of use (25 or 50 times etc.)
3. Inserting a Logo of the company
4. Limit on size of file (max. 1 MB or so)
5. Restricting some features
6. Restricting the duration of media files (1 min. playback)
Of-course, spoiling your valuable image by inserting a Logo on every finished work is the worst among them.