I downloaded a document onto my Apple IPad Pro (December 2018 version) running IoS 12.4. It is in the 'On This iPad' location showing as 'application-pdf.pdf.pdf'. When I try to open it it shows " Could not open due to an unknown error". It will not

Not really sure what you are asking and not sure if this has anything to do with Adobe Acrobat Reader for iPad + iPhone.

You should post your question on how to delete files, or Programs (Apps), from an iPad over on the Apple iPad forum.

The people on the Apple forum are better equipped to answer question of how iOS works.

Just to complete my comments above:

It will not let me take any actions. When I try to delete it, it shows: "Unable to delete".

I have tried reopening the App and restarting the iPad.

HOW DO I DELETE THIS DOCUMENT?