Access Denied for Request Signatures

I am using Acrobat Standard DC.  When I click on Request Signatures and then 'Specify Where to Sign', it says “Access Denied. You do not have access to this service. Please contact your IT Administrator to gain access. Please let me know how access can be gained.”

Firstly, could someone confirm that Acrobat Standard DC includes the 'Request Signatures' function. This page seems to say that it does: https://acrobat.adobe.com/uk/en/acrobat/pricing/compare-versions.html

But someone in the Adobe online chat said it doesn't. 

Secondly, presuming that 'Request Signatures' is included, please can someone help me to resolve this problem.