Can you set up a repeatable batch to append a file from one folder the the files in another folder?

Using the Actions, I can set up a batch appending a specific file to a set of files in a folder, but is there any way to set it up so that whatever file is in a folder (it’s always just one) is appended to whatever files are in a second folder?

i.e., I want to attach the one translation certificate PDF that I place in the CERTIFICATE folder to the translated PDFs in TRANSLATIONS folder, and output the merged files to the OUTPUT folder. When I’m done with that batch, I can just delete the files in the CERTIFICATE folder and TRANSLATIONS folder, put new files in there, and run the Action to get the new outputs--all without having to Edit the Action.