A simple way to find out the number of occurrences of a word is to replace it with itself. When you click the Replace All button, Word reports the number of replacements.
For a single document, you can use the macro in the article
How to find out, using VBA, how many replacements Word made during a Find
& Replace All.
Since you want to process all the documents in a folder, you would have to combine this with code that iterates through multiple documents. This is not a trivial task, of course.