Whenever I attempt to use pdftk invoking the "output" argument, it crashes with the following Java exceptions:

Unhandled Java Exception in create_output():
Unhandled Java Exception in main():
java.lang.NullPointerException
at gnu.gcj.runtime.NameFinder.lookup(libgcj.so.14)
at java.lang.VMThrowable.getStackTrace(libgcj.so.14)
at java.lang.Throwable.getStackTrace(libgcj.so.14)
at java.lang.Throwable.stackTraceString(libgcj.so.14)
at java.lang.Throwable.printStackTrace(libgcj.so.14)
at java.lang.Throwable.printStackTrace(libgcj.so.14)

This situation has persisted for a long time but went away for a short time between two successive dnf updates. I would like to get it solved.

My immediate problem is trying to attach a user_pw to a file, but I have not been able to find a utility other than pdftk to do this for me. Any suggestions would be welcom, but I would really like to restore pdftk to working order as I have quite a few scripts that use it.

Can you, just for completeness, show us how you invoked pdftk with all options?

A Nullpointer-Exception in the create_output() routine cannot have more than two reasons, one of which we can try to exclude.

Here is an example:
pdftk type1*.pdf type2*.pdf type3*.pdf output portfolio.pdf user_pw 1234

However it seems that any invocation of pdftk that includes the "output" argument fails in the same way.

Cheers.

Okay, my personal opinion is, that you should try with a different java version. Before I throw stones at pdftk, I suggest that you install a different java environment. OpenJDK 8 or 7 should be okay. You only need the JRE.

There is a bug description on bugs.launchpad.net, but it dates from 2011.