For better understanding, would you mind elaborating it a little further like:
1- Have you marked the file with the Star on the desktop over Document Cloud files?
2- Have you not been able to change the name of the invoice which are started only, or are you referring to any file?
If the file was sent by email, you probably need to save it locally to rename it.
A bit more detail would be super helpful. Like,
Hope you are doing well. Sorry for your experience with Acrobat Online Service.
To clarify, if you have received a file from another Acrobat user over Email, you will not be able to change the name of the file unless the original sharer does so. You will have to create a local copy to achieve this.
If you are trying to change the name of a saved copy file through the web, you might want to click the three dots on the right-hand side of the file name and then select 'Rename' (screenshot attached for reference):
Hope this helps.