Zoho CRM: get invoice PDF from custom button function

Zoho CRM: get invoice PDF from custom button function

Hello,
I'm developing an extension for Zoho CRM to sign documents via an external service.

I have a custom connector which calls the external service and submits a PDF to be signed.

I have a custom button in the Invoice Details page which triggers the appropriate API of my custom connector.

How to I retrieve the invoice PDF from the button function (Deluge)?

Also: is it possible to show a popup form to the user when he clicks my button, so that he may, for example, select the sign format?

Thanks, best regards
Fernando