Must signature be validated every time file opened?

Hello and thanks in advance for your assistance:

I have Acrobat Standard 9:

I was sent a file that when opened says "at least one signature requires validating"

I went through the process - 1) find signature, right-click, show properties 2) show certificate 3) trust tab, add to trusted 4) validate and after - it says "signed and all signature are valid"

At this point, I save the file under a new filename.

Then, when I open that same file again, I get the message again "at least one signature requires validating" (I don't need to go through the whole process again - just have to right-click, validate.

My question is : Is this right, that I should have to "validate" signatures everytime I open this file? Or is there something I need to do to...