How can I obtain a digital certificate from recipients?

[Joe Needs Help]

I've written a book in pdf and would like to share it with my supporters so that only they can open it.  I don't want to use password protection because if the password is shared, others can open it.  Adobe Acrobat has a way to encrypt a document using a digital certificate.  I can do that.  What I can't find anywhere is how to request the digital ID of my intended recipients.  Older versions had a way to request others' public key via email.  Does anyone know how I can share my certificate-encrypted pdf with others on a list and allow only those others to open it?  Is there a way to request that recipients set up a digital ID that doesn't require a lot of sophistication by the recipients?  Any help would be appreciated.

[Bernd Alheit]

You must ask the recipients for the public keys.

[Joe Needs Help]

Once upon a time, Adobe would ask for a list of email addresses and then prompt the adressees through the process of obtaining a digital certificate.  That put a digital id on their device, ensuring that only they would be able to open the encoded file.  It appears that Adobe has dropped this option.  I think what you are telling me is that I need each recipient to go through the hassle of creating a digital id.  This will be impossible for many who do not have the appropriate software.  It looks to me like the encrypt via certificate option is fairly useless to me.  Thanks for your reply.

[margueritek]

Have each of the recipients send you a PDF that has been digitally signed with their certificate. You can then examine the signature (signature properties) and export the public key certificate to a file on your machine. They can use a self-signed certificate, if that is acceptable to you.

[Joe Needs Help]

That won't be possible.  Many of my recipients have only Adobe Reader.  I was hoping that Adobe had a better option.  Thank you for your reply.