You must be on Fincent’s Starting, Growing, or Thriving plan to access Files.
A document in Files has a “bill” tag only if it’s linked to a bill. You cannot delete a tagged document.
To delete a document that’s linked to a bill, go to "Pay" and then "To be Paid," edit the bill, and delete the attachment (this removes the tag from your document). Now, you can delete the document from Files.