I'd contact the state work comp division , if a claim gets settled or closed they should have it recorded and on the record.
For oregon you can search the state website for wc judgements.
I don't know if the wc ins company would send you copies of everything to date, but it's worth a try to ask.
Do you have a new atty now, or none??
The old atty should have copies to turn over to you also...if not contact the state wc div or the state bar...
If you can find your contract with that atty look thru it for details, maybe it mentioned giving him power to sign things??
But basically you need to find out exactly what happened and if someone did forge your name and to do that you need the paperwork.
I was always sent copies and if things needed to be signed I got that and a stamped /addressed envelope to return it, or faxed it.
Did you do a search of that attys name to see if any other negatives came up? you might find out things that way too.
Also check him on that state's bar association page.