.DOC and .XLS are old formats. Please can they be updated to the latest versions, which have been around for a while now.
Screenshot from Registration - Reports - Individual Register Report.
Seems to be the same choice of report formats throughout the Registration module.
Thank you for bringing this to our attention. We worked to change the file formats several years ago, but it would appear that these were missed. Please would you raise a ticket with the support desk to raise this as a bug - you can mention that you raised this on the Ideas Portal and I redirected you to the support desk.