Hey Chris,
Sorry for the late respons.
The original macro was created by @JimmyHartington: Merging PDF Documents - #3 by csmltd
I get this output:
pdftk "/Users/hl/Desktop/REF"*.pdf cat output "/Users/hl/Desktop"/"REF".pdf
BTW: Since I'll always use this macro to create a PDF file /Users/hl/Dropbox/CT/Jobs/REF.pdf from all files in the folder /Users/hl/Desktop/REF, the Finder selection part can be omitted.
I found that with Big Sur there's now a dedicated Quick Action: How to Combine Files Into a PDF on Mac