Cannot attach Office files to emails in Outlook (other filetypes are okay)

Suddenly I cannot attach Word, Excel, Powerpoint files using the normal attach button. PDFs and images are fine. Most online advice says to check 'sharing preferences' for attachments. I can see screenshots online of the options that I'm supposed to see, but the options are not presented when I go into the attachments section and look at sharing preferences. I get the option to add a storage account, and to choose a warning message if an attachment may be missing, but that's it. No options at all to change the way attachments are handled. Any suggestions?