Hi again!
First of all, thank you for the detailed post. It makes things easier.
Please also note the attachment control in my example is for the purpose of attaching several files, not just one
I think you do not ned to pass all the file path/names or identifiers, your current design allows an (imo) easier approach to your current challenge: just make your Power App pass the ID of your record to execute your Power Automate Flow.
THen you can implement a 'Get item' using the record ID to get the data for the covering letter
Then you can implement a 'Get files (properties only)' and use record ID to filter on column Reference, so you just get the files you want to target, and not all the library files. You can apply the filter by means of a more efficient Filter Query ODATA expression in the 'Get files (properties only)' or by means of a more flexible 'Filter Array' independent action block.
Then you can follow a similar approach to the one in the thread I suggested in my first post: add an 'Apply to each' with the results filtered as its input, inside it add both a Get File Content, and an 'Append to Array' (please remember to initialize the variable first)
Now add 'Send an email' out of the 'Apply to each, at the bottom of your PA flow
THere is a third approach for the filtering, that is to use a Condition inside your apply to Each, as in this post.
Hope this helps
