False negative

[Shorouq]

I created a pdf file days ago by combining multiple images and compressing it using adobe acrobat PC ver. It looked fine at the time. Now when I open it, it's a completely different file. It has the content of another pdf file on my pc but has the size of the original one, and yet worse, it has a creepy cyphered message? It freaked the sh*t out of me. I scanned the file using Kaspersky, but the results were negative: "no threats". I ran a quick scan, also turned out negative. I'm currently running the full scan. Could there be a virus on my PC that Kaspersky isn't able to detect? What do I do?

[CLEsports]

Maybe it's a corrupted file? If you open it in Acrobat, does it show anything differently?

Edited September 30 by CLEsports
update

[harlan4096]

Also, upload to https://www.virustotal.com/gui/home/upload