Hi @Anonymous,
You could get all files information first by using Get files(properties only).
Then use Filter array to filter files, if the file name with the extension ends with the expected file format.
Use endswith() function to make a decision.
Formula reference:
@or(endswith(item()?['{FilenameWithExtension}'], '.docx'),endswith(item()?['{FilenameWithExtension}'], '.doc'),endswith(item()?['{FilenameWithExtension}'], '.xls'),endswith(item()?['{FilenameWithExtension}'], '.xlsx'),endswith(item()?['{FilenameWithExtension}'], '.ppt'),endswith(item()?['{FilenameWithExtension}'], '.pptx'))
Image reference:

Please take a try.
Best Regards,
Barry