How to create formfield in transient document

We have document generated in our end with placeholders in docx file, but adobe sign not recognize those after upload. and we can't go with library as we have dynamic content with this placeholder generated on runtime using external library. 

Is there any easy way to use the docx fields / any way we can place the form fields using label text,or anything using transient document. We looking mainly for Signature block to be placed in such position.

Thansk in advance.