checking pdf document during web testing

Hi everybody,

I need your help. One of my test contains to check a training record. Let me tell you the process:

Actually I am working on web testing but at one point you should click a link but this link is not a web page link, it is .pdf document link. So a new page opens with a new tab. What I want to do, I want to check the certificate if the name of the trainer or name of the training is correct. But the system can not recognise the page which contains a pdf document and I try to put some property check points for checking the certificate, I can create but than when I start to automate test, and you can see the system message in the screenshot attached.