I don't think that this one is signed by ABBA. Agnetha does not look close to what I have seen before.Here is one from Bjorn and Benny that I got in person to compare.
It does not look like authentic ABBA autographs. Probably signed by someone in the Polar Music office, as was common practice in the 70s when ABBA were too busy to sign hundreds of autographs to send out to fan clubs, etc.