Layered PDF File Won't Open in Photoshop, Says File Format Not Supported

Hey all

I designed a layered file in Photoshop and saved it as a CMYK PDF with layers open, I was working on it fine yesterday but today it refuses to open, it's not my software as I opened another few files made the exact same way and saved the same way and they're fine.

Error message when I try to open it is the following: "Couldn't open file [name.pdf] because the file is not compatible with this version of Photoshop"

I have the latest version on my PC so not sure how to fix it, I tried converting it online to both PSD and TIFF files but when they opened the file wasn't layered anymore and I couldn't use it.

Any advice? I've tried reverting to an older veriosn of Photoshop, opening it on my wife's PC, converting the file, opening it in Bridge and exporting it and resetting the defaults on Photoshop. Can't figure it out at all.

Thanks in advance.