The following required executable could not be found on the server: pdftk

When trying to view a pdf in collectives - it opens a new viewer but nothing appears.
When trying to download a pdf I get
The following required executable could not be found on the server: pdftk
any advice?

The first might be this, which just has a solution merged yesterday for it:

But the quoted matter may be something else. The only app I see that might use that binary is one called pdfdraw / “PDF Annotations”:

Maybe that’s a clue.