PDF does not show digital signature

Do you have a PDF file which does not display digital signature? Read this thread to know how you can solve this problem.

I have a pdf file that was sent to me by an official organisation. At the bottom of the pdf there needs to be a digital signature of the authorized person for this pdf to be valid. However, this place just shows a 'yellow question mark' instead of the actual signature. It also says, 'signature not verified'.

The person who's sent it confirms that there's nothing wrong with the pdf that they've sent. Can someone please tell me how to get it activated on my PC? Is there a setting that I need to change on my system to be able to view the signature?