What should I do with the fax?

Hint 1 of 5:

I can think of one person who would be interested in a translation of
Ludwig's diary.

Hint 2 of 5:

Nope, not Gerde.

Hint 3 of 5:

Nope, not Mrs. Smith.

Hint 4 of 5:

Nope, not the old sourpuss at the Ludwig Museum.

Hint 5 of 5:

That should narrow down the list of eligible candidates.