mouse and copy paste not working in a software

Desktop, or Laptop?

Get an inexpensive mouse or borrow one and try a different mouse.

If laptop, there is probably a mouse driver. Update that.

the mouse doesn't work in it

Does it work in other programs? What program are you using? More information would be helpful.

Maybe the right click doesn't work that's why he can't reach copy option. Remember you can always copy - paste using keyboard
Ctrl + C = Copy
Ctrl + V = Paste

Maybe the source is a secured PDF.

For the attention of experts looking at this question, the only topic area that had been added to the original question was "Software".  To try and raise more attention, given that the question was set to Low Priority when in fact it seems to be High Priority, it was me who tried to second guess possible applications by adding:  Microsoft Office, Word Processors, Microsoft Word, and Hardware.  The asker has not yet told us what application is in use when this problem manifests itself.

Here is a list of useful keyboard shortcuts in MS Word.

https://www.veodin.com/2012/09/03/20-microsoft-word-shortcut-keys-that-you-would-actually-use/

Problem unclear

What software are you using?

test the "bad"  mouse obn a working system
or test with a known good mouse on your system