pdfcomment.sty: tlmgr says it's installed, but latex document doesn't find it

[John Coppens]

Hi all.

I created a new LyX document and imported the 'orbd.tex' file from a package
I wanted to use (https://vtechworks.lib.vt.edu/bitstream/handle/10919/84164/LaTeX%20sourcefiles.zip?sequence=16&isAllowed=y) and modify some things.

tlmgr list --only-installed

lists the pdfcomment.sty file, but trying to render the document I get the 
message:

LaTex error: file pdfcomment.sty not found.

Do I have to define some path for LyX to find the document?

LyX 2.3.6.1 on Slackware64-current

John