Was going to point you to the bug tracker issue for this (https://luceeserver.atlassian.net/browse/LDEV-1300), but I see you already found it
I also see there you asked where to get it - you can update the PDF extension from the Server Admin under Extensions -> Applications. Current version (I have) is 184.108.40.206 (1 version higher than the fixed version).
Looks like you may also have to be at Lucee version 220.127.116.11, which means going to the 'Snapshots' update provider instead of 'Releases'. If you're on a production server then I don't suggest doing that though.
On a production server I would probably downgrade Lucee to 18.104.22.168 and leave the PDF extension as-is for now and wait for the next release (which should be coming soon).
Or, you can try the snapshot and if nothing else breaks leave it at that snapshot level until the next release. It's trickier on a production server, so perhaps fire up a dev server and try those combinations to see which works best first.
If you're not on a production server, then just upgrade the PDF extesnion and take Lucee up to the latest snapshot level (22.214.171.124-SNAPSHOT as of this writing) and you should be good to go.