Copy / Past file form CMYK to CMYK color change

[Speedpro]

In Illustrator when I copy a file from an open CMYK file and paste into another CMYK file the color changes, gets darker or lighter. I am using a pantone spot color and it reads as the pantone color in both files but the CMYK values change. Anyone know why this would be happning?

Thanks!

[Ton Frederiks]

Check if the document color profile is the same in both documents (to be found at the bottom of your window)

And turn on the warnings in your Color Settings to see what is happening.

[Speedpro]

They both say untagged CMYK.

I turned the warnings on.

[Ton Frederiks]

And do you get a warning when you copy and paste between documents?

[Kurt Gold]

Can you check if perhaps one document is in Overprint Preview mode (see View menu), but the other one not?