PDF limit access to specific recipients

[Verena123]

I would like to restrict the access to a pdf to specific participants (internals and externals of my organization). With the "Encrypt with Certificate" option I tried to select the recipients via the search function but always get the notification not found when I enter the email address. What do I need to do different? Is there another functionality in Acrobat pro to restrict the pdf access to only specific people? Thank you. 

[Bernd Alheit]

You need the public key of the participants.