Ios11.0.1 “Cannot save file” error saving from Office apps to Dropbox

Thanks for the screenshots! I'm able to reproduce this. The flow you're using is specific to Microsoft Word. It's not the Files app and it's not any Dropbox extensions. The error message being shown is from Word, so I would file a bug with Microsoft. It definitely looks like a bug.

While playing with it, I got the same error as you most of the time, but sometimes it did manage to save. Also sometimes when I get the error, the file still got saved to Dropbox, but the contents are missing (file size 0 bytes).

I tried linking a new Dropbox account and was able to save the pdf multiple times without it showing that error. You could try signing out then in of the same Dropbox account from Word. You can unlink the account by going to the home screen in Microsoft Word, and tapping your name in the top left corner, then swiping left on the Dropbox account in the modal that pops up. Then you can add it again with Add a Service in the same modal.

If you have iOS 11 and iPad you should also be able to save into the Files app via the "... More" location. However when I tried that Microsoft Word prompted me to get an Office 365 subscription so I think it is a paid feature.

If you're ok with saving just the docx (and not exporting it to pdf), you can select Send a Copy instead of Export, then select Send with Another App. In the modal that pops up, select Save to Dropbox in the bottom row and that should trigger our Action Extension, allowing you to save the docx into Dropbox (you will need to have the Dropbox app installed and be signed in). You can also optionally select Copy to Dropbox in the top row to actually open the Dropbox app to perform the save.