Digital Signature (Digital ID) on iPad/iPhone

Hello there. 

I spent all afternoon searching for a way to fill and sign a legal-form type pdf with a digital id but I found no way to do this. I downloaded tons of apps from the AppStore and nothing did the trick. Is there really no way to do this via Adobe Reader on powerful devices such as iPads Pro/iPhone 11/12? I mean the 2018 iPad Pro's A12X can handle macos big sur but you cannot port the desktop Adobe Reader app to iPadOS?