From the Introduction:
When the GURPS Basic Set, Third Edition was released, we also released GURPS Update, a conversion guide so that those with GURPS Basic Set, Second Edition could play Third Edition games. Now that Fourth Edition is here, we're doing something similar. Updating all the new rules would require a book almost as big as the entire GURPS Basic Set, Fourth Edition!
This edition of GURPS Update is designed to help you convert characters from Third to Fourth Edition rules with a minimum of fuss. It doesn't go into all the new rules - you'll need the full GURPS Basic Set, Fourth Edition for that. What it does is ease the transition for existing campaigns and characters, so you can convert the characters quickly and continue to use them with the new Fourth Edition rules. You can also use GURPS Update as a quick reference to what has changed in character creation, so you don't have to laboriously compare the Third and Fourth Edition rule books yourself.
This update only deals with material from GURPS Basic Set, Third Edition
and GURPS Compendium I
. It doesn't try to cover world-specific rules only published in sourcebooks, so you won't find conversion rules for the Coat of Slime advantage or Dexitroboping skill. If you really need those, there are tools and suggestions in the Fourth Edition rules to help you.
This PDF updates GURPS 3rd edition rules to the 4th edition. There are no copyright dates, product numbers, or other identifers listed on the product. It is available directly through the Steve Jackson Games web site.