Digital certificate

That is impossible.

Adobe Acrobat Pro DC only runs in macOS and Microsoft Windows desktop operating systems.

iOS devices can only accept the free Adobe Reader Mobile app.

You are only able to unlock premium editing features when you purchase a subscription of Adobe Acrobat Pro DC.

To unlock these premium editing features you need to sign in in the Reader Mobile app with the AdobeID  associated with that subscription.

Also, the use of self-signed certificates and / or smart card readers that allows grabbing a root certificate from a certificate store to apply it in a digital signature field, is also not possible in the Reader Mobile app.

You need to incorporate electronic signatures instead.

This is done with the  E-Sign workflow , which is accessible via the Adobe Sign app.

You will need to also install Adobe Sign app and incorporate this workflow if you will be using your iOS device to sign documents electronically.