Cannot Open Excel Doc Attached Inside PDF

A year ago I started attaching supplementary information (excel doc) inside of a pdf by way of the "comment > add new attachment" feature. I never had problems opening the pdf or attached excel doc, and neither did the recipients. However, this has changed. More and more people are having issues opening these excel documents (.xlsm).

Is it because of the file type? Is there a way I can change the trusted documents to include these types? The Edit > Preferences > Trust Manager >PDF File Attachments "Restore" button is greyed out and no longer an option. This fixed the problems on occasion, but I am still in search of a full fix so my recipients can view the attached document.