is there role for window registry in trial software(number of days allowed) if so then how?

Answer 1

Some trial software uses the registry to store stuff like the date the software was first installed, the number of days left on the install, etc. The date first installed is somewhat sneaky as the software will check the key value vs the current date on your system and refuse to install if a certain number of days have elapsed.
It varies from one software to another. In practice using the registry exclusively is an incredibly weak way to handle this sort of thing as it's quite simple to delete the registry key in question and reinstall the software.