ITextSharp: AcroForm field value disappears after signing PDF document

I have some input fields/AcroFields in my pdf.

Now, I want to send this pdf using adobe sign.

The problem I'm facing is that, when I send it, I'm not getting signature field and if I send it with removing acrofields, It works fine.

I'm placing {{Sig_es_:signer1:signature}} to get signature field.