Text removed from technical documents where {{ }} is used

I have a techical document that I need to send for signature.  I have text entered like this:

studies/{{studyoid}}/datasets/{{Form}}

Adobe Sign is removing the text {{studyoid}} and {{Form}} and putting in a text box. When I remove the text box the required text as above is deleted.

How do I stop this happening?  The document must have this information present before it can be signed.

Thanks!