What can you do to deal with Locked PDF's? Well here are some simple solutions to try:
Try printing it to a PDF. This often allows you to bypass the locked issues, but doesn't always work.
Use PDF Key Pro to unlock your PDF. By far the best third party app I have found and seems to work almost every time. Affordable 1 time purchase. I have owned my license for about 10 years. https://pay.paddle.com/checkout/504065?coupon=CURTEK17832
Go back to the source and ask for an unlocked/unsigned version of the same file. Never hurts to ask!