remove duplicate documents from iMac

Gemini is a good program that I use.

I would begin by using the Mac App store to see if there is a utility available. You can also use Finder to do this, please also search using Google. For example I found this article that you may find helpful:

https://www.macworld.co.uk/how-to/find-delete-duplicate-files-mac-3679414/#:~:text=Manually%20searching%20for%20duplicates%20with,in%20the%20upper%2Dright%20corner.