When I add a digital signature field it does not bring up the draw signature feature

[danh81449429]

I'm using Adobe Acrobat Pro DC v 2015.023.20070

I have opened up an xml file which is designed as a sign off sheet. I have added a signature field box in to the section which requires a digital signature, but when I open it up in Adobe Acrobat Reader and click on the signature field, it just starts the cursor, and allows for entering text; on tutorials I have seen it should bring up the 'draw signature' feature and allow you to sign it.