Copy Ending.pdf to one directory (say C:\End) and all the other PDFs to another directory.
At the command prompt type pdftk and press Enter. If you receive an error like 'pdftk' is not recognized as an internal or external command, operable program or batch file, you'll need to add the PDFtk installation directory to your PATH or specify the full path to pdftk.exe in the command below.
Alternatively, since the app is pretty much portable and I don't see any registry keys or miscellaneous files being created/littered about the system, you can simply copy pdftk.exe from the installation directory to the directory where your PDFs reside.
At the command prompt run the following command in the directory with the PDFs you want to append Ending.pdf to:
for %a in (*.pdf) do pdftk "%~a" "C:\End\Ending.pdf" cat output "%~na (Joined)%~xa"