Using an EXISTS filter, you could produce a Document report that only returns documents in a folder with a specific folder name. The following text mode would enable you to do this.
EXISTS:a:folder:name=The Name Of Your Doc Folder Here
If it is a very specific folder you are looking at, I would also add an additional filter rule to only look at documents on a specific project or task . This will ensure that if there are other document folders in your instance that are named the same, those documents appear in your report.