Digital and e-signatures are not compatible in Acrobat because addition of an e-signature may break existing digital signature. It depends on how your digital signature is created. If it has a lock then you cannot add anything to the document.There are other ways to specify permissions associated with a digital signature, usually with certifying signature, and when there is a permissions conflict you cannot add e-signature to a digitally signed PDF.
In order to get that option back, you'll have to remove the digital signature field, not just reset it.
Unfortunately, it has nothing to do with the document itself.
I am not able to set up an electronic signature, thus it is not that I want to have both signatures on the document.
I cannot remove the digital signature field either.