Merging document and (back) cover page

Hi,

Apologies, bit of a newbie to this but trying to use the Adobe PDF Services to replace some functionality in a Power Automate flow that we were previously using Muhimbi for. It's basically a document approval process but later in the flow a table with the document's metadata is pulled out of a separate document (a Word doc) and appended to the end of the main document (a pdf doc). This screenshot from the original flow might give you a bit of an idea how it was working:

I'm trying to use the "Merge PDFs" connector to do the same sort of thing and thought I would just be able to put the content values from each document in as the file content - however got a file corruption error:

So then did some reading on these forums and thought I might need to use an array, so have given this a go but not having much success there either:

I know this latter issue is not strictly Adobe-related but why does it want the content value to be an array and not an item? I thought the point of an array was to collect a group of items together...

Am I on completely the wrong track?

Many thanks in advance