Hello aspirant,

You are not allowed to sign the admit card before entering examination hall. They have made it very clear in the instructions of afmit card and cirrculum, these are some rules which you have to strictly follow to avoid any discrepancy as they may violate your appearance in the examination. Please follow all the instruction written on admitcard.

Best of luck!!

Yes. You have to read, understand the contents and sign the declaration with place and date alongside the space for the photograph. 

You can find more relevant informations in the Aiims official page, on the tab, "Important instructions regarding Aiims mbbs entrance examinations -2019"