I tried to open a pdf file as usual on my MacBook (os 10.11.6) and it didn't open. I tried to open the Preview app from the Applications Folder; this opened a new window, the purpose being to select and open the preview App. when I clicked the "open" button, a bunch of new window started to appear, all with AAD in the title bar. I am unable to open any other pdf files using Preview. I use Preview regularly. I hope someone can help with this.
Hank
Hank