I imported a step file in solidworks but all mates were lost. Actually, the assembly stays as it is needed to be, but there is no restriction. So I can move every part as I wish.
Is there any way to apply the mates on this file?
For the first question of keeping mates: No
For the second question of applying mates: Yes. You apply new mates in a solidworks assembly.
If there are some parts that do not need to move, consider using the Fix option to hold them in their current position. No need to add mates, if the part does not need to move.
Thanks for your helpful comment. I did not know this, and it was a weird situation for me.