Adobe Welcome back screen. Is it Malware?

Every time I try to open a PDF I get a pop-up with the Adobe logo that says Welcome back.  (I just opened a PDF a day or two ago so I have not been "gone.")  It then lists an unfamiliar email address under "Personal Account" and says that I've previously signed in with that address.  Um, NO.  And it invites me to sign in with another account/PW.  This just looks suspicious to me, like it could be malware.  (I am using a Mac.)

There's a red close box in the upper left corner but it doesn't work. The only way to disable this is to force quit but then it appears again if I try to open a PDF.  I will try to attach a screen shot.

Does anyone know if this is legit and I should just enter my actual account email and PW to get rid of it?  Thanks.