Where to Enter Licence key.

Hi

I downloaded the Adobe Reader Android mobile app to open a protected pdf file .  The pdf file opened but the licence key form field was not active when the file opened.

How do I type in the licence key?

Really frustrated.

I can type in the licence key on to file on my PC and open the file but cannot do so on my Galaxy Note 2014 Edition. Why?

Help. l need this file on the go.