If you are talking about custom forms or reports of the forms and reports in the system then they all use the works tables associated with the form or report name.

What I'm trying to find is what .rpt file is tied to what custom report or form. As an example, I have a report in my MAS90\Reports folder named arw109_custom.rpt. Is there a way to find out what the 100+ files named like this are linked to in Sage?

Try querying SY_ReportSetting and look for ReportID ending in CUSTOM.RPT.

In all modules on the business framework the name of the report is the name of the file.  That file I suspect is an old custom.  Rather than go through DFDM as Kevin is showing just pull the file with excel and go through it. It is available through ODBC

Any reason you can't open it up in the Crystal Reports Designer and look at the Database Expert? That will not only tell you the data source but any linking if there are multiple tables.

I could but I'm not looking for data sources. I'm just trying to tie the name of the custom report in Sage with the file name so that I can clean up unused reports and reclaim server disk space.

Can you find them in Report Manager?
Can you run them from the Sage Custom Reports menu? If so you can export to PDF and when you go to save it the pdf file it creates will have the same name as the .rpt file.

That works one by one, but the question was to come up with a list, and an Excel query of the table I mentioned above will do that.