Maybe try opening it on a public computer, if its an honest pdf, then should open and then you know its safe. You really don't want to open a suspicious file that infects your laptop or phone.

If its legit, you should have a proper go at the person, why give so little info in main email, baiting tou to open a file. There should be some information on who it is, a website, abit of background, or something. Need some info to verify who it is atleast! "Trust, but verify" is out motto right.

If its legit, the first 10 minutes of interview should emphasise how to approach someone correctly when asking for an interview and not make them so para and nervous that they being scammed!