That's a very simple question but the answer is very complicated.
It depends what you mean by 'deeds' and what period of time you are talking about.
If you mean title deeds for property, the documents recording changes of ownership of land, buildings etc are called Sasines. Most of these are in the National Records of Scotland, and are indexed after a fashion. However some burghs kept their own Registers of Sasines, and I don't know if this applies to Cupar and if so where the Cupar Sasines are - though it wouldn't be hard to find out. Some older sasines have not survived at all. See
https://www.rootschat.com/forum/index.php?topic=26232.0 for more information about the sasines. What it boils down to is that if you are looking for (a) sasine(s) in the County of Fife, and assuming that the one(s) you want have survived and are in the NRS, it shouldn't take very long to find it/them.
See also
https://www.nrscotland.gov.uk/research/research-guides/research-guides-a-z/sasinesIf, on the other hand, you are looking for some other sort of deed, the Registers of Deeds are in chronological order, and only some years are indexed (in paper volumes, not digitised). If, for example, you are looking for a deed in the early 18th century, and it's not in any of the years for which an index is available, it would be necessary to order all the relevant books of original documents and read through them page by page. That could be a very long job as each book can have hundreds of pages (and some of the handwriting can be difficult to decipher).
See also
https://www.nrscotland.gov.uk/research/research-guides/research-guides-a-z/deedsThere are lots of other wrinkles but those will do for a start.
So please expand on your original request - full names, how they are connected to one another, all associated dates, which parish you think they are associated with, and what sort of deed. The more detail you provide, the easier it will be to assess the likelihood or ease of finding what you want, and where to look for it.