Acrobat DC Pro check folders and subfolders for PDF files only

Have a custom action setup to reduce pdf file size in a specific folder and its subfolders.  However, I need the action to skip over all other file types that are NOT pdf files.  If it's a javascript command that needs to be inserted into the action, that would be fine.  But haven't found a way to accomplish this. Current action (without javascript command) fires error message when trying to open, .docx, .xlsx, .txt, etc. files.

Any help would be greatly appreciated - even if it's to tell me to stop trying, it cannot be done.  Then I will move on.

Thanks.