As part of the year end procedures, I inadvertently selected to purge vendor detail for past years. However I have two complete backup copies of my hard drive data so I want to restore the adagio data from before the year end. Can I just copy the files from the backed softrak/data directory and replace ones in my C drive?

Move all the files you don't want (likely all the files in the data Folder) to another Folder before copying the backup files into place. After the copy, run Data Integrity Checks in all the modules, and print the major reports to confirm the numbers are what you expect.

It's usually well worthwhile checking with your Adagio consultant when you find yourself in this position, since a mistake in the process can generate days and days of work.