Generated documents, and the line at the bottom of them
Agreements, disclosures, reports and settlement documents are generated rather than filled in by hand.
Your letterhead, on every one
The letterhead is applied by the engine rather than by each document type. That is an implementation choice with a consequence you care about: a document type added next year cannot be the one that forgot.
The provenance line
At the bottom of every document is a line saying what it was generated from and when.
It is there because a printed document outlives the screen it came from. Six months later somebody is holding a page and asking which version of which record produced it, and the honest answer needs to be on the page rather than reconstructed.
What proves it worked
Generate the same document twice from a record you have not touched in between. The two files are identical, byte for byte.
That is a stronger property than it sounds. It means nothing in the document depends on the time it was generated, the machine that generated it, or the order something happened to be read in. If two generations differ, something in the document is not coming from the record, and that is worth finding.
Why that matters to you
Because it makes "this is the document we sent" checkable. A document you can regenerate and compare is evidence. A document that comes out slightly different each time cannot be compared to anything.
Changing a document after it is generated
You do not edit a generated document. You change the record and generate again, which produces a new document with a new provenance line. The old one stays as it was.
That is deliberate. A generated document that can be edited afterwards is a document whose provenance line is a claim rather than a fact.
If your letterhead is wrong
It comes from your branding settings. Fix it there and regenerate. Documents already issued keep the letterhead they were issued with, which is correct: reprinting an old document with today's branding would misrepresent what the recipient received.