Help please using pdftk - where is my error please?

Further to this I tried my HP Z640 Leap 15.4 machine and it too works perfectly.
Returned to IBM server and tried again. First try new errors but I had been trying on subject files which have been moved to pCloud so went to originals (which is what I had been working on yesterday) and this morning all good and pdftk working as expected.
There have been updates every day which might have caused problem but seems unlikely. One of the joys!

Hi guys, forgive me, but I often use pdftk to do the same thing, but with a different “sintax”.
Maybe, I’m wrong (in case blame on me), but I use this command:

pdftk A=page1.pdf B=page2.pdf C=page3.pdf cat A B C output combined.pdf

Does it work even for you?