As a point of interest, here are all of the file types used in connection with Acrobat:
https://helpx.adobe.com/acrobat/kb/supported-file-formats-acrobat-reader.html
None are .skb. Also, here’s another time it happened to someone with SketchUp:
https://forums.sketchup.com/t/skb-files-turn-into-pdf-in-my-pc/45559