Signature Field Missing When Form Sent As PDF

I am having the same issue.   

I have many staff that are pretty much computer illiterate.  I was trying to send the fillable form to them via Outlook email as checking their email is pretty much the most our staff can do on a computer. 

I had created the fillable form with fields where they needed to be, and had a signature field.  I even had a submit button so they could fill out the form and then click submit so it would come to me automatically as staff do not know, or depending on location, do not have the ability to scan and send back to me. 

Is this not an ability to do with Adobe at all?   

Staff just aren't able to do this as these instructions show; therefore, they typically print it off, fill it out, and then the paper sits around for weeks until someone who has the knowledge is able to scan and email to me.  Very inefficient and I was trying to make it easy for everyone.

Without analyzing the PDF itself I see two possible reasons: 

• The person you've emailed the PDF to has opened it in a viewer that does not support applying digital signatures. In that case the signature field may not be selectable at all, and the appearance of an empty signature field usually is blank. 
• When creating the form you created it for filling in and signing via the Acrobat Sign service. Those forms are a bit different from those created for use on the local computer. In particular signature fields are different. You select this form type by having the check box "This form requires signatures" checked when starting to create the form.

What do you mean by "downloaded"?