Tengo instalado el certificado en el iphone se puede firmar digitalmente un pdf con el iphone.
Hope you are doing well.
Per the description, I understand that you want to digitally sign a PDF from your iPhone.
This feature is available on the desktop version of the application and not on mobile.
I suggest you fill out the feedback form. Filling the form ensures that your feedback reaches out directly to the product team for them to look into it and try to implement it in the upcoming updates: https://acrobat.uservoice.com/
Hope this clarifies the point.