When to use the "Process Fields"?

Question

Hi, I have a simple form with some text fields and a couple of Signature fields. 
All is working fine in the WorkSpace.
The Process / Workflow is also simple, Initiator --> User --> User.
But I want the user to be able to submit the form outside of the WorkSpace.  ie. the user receives the form as an attachment to the Notification email from the server, user opens the attached PDF, clicks the submit button, and the workflow continues on to the next step after the server receives the email from the user.
I read it somewhere that, in order to do this, I will need to drag the Process Fields block onto the form.
So I did that.
Before trying the email-submit, I wanted to make sure that it still works in the WorkSpace. 
Unfortunately, it doesn't work anymore.
When the "User" (2nd and 3rd steps in the workflow shown above) opens the workitem, the PDF form was not displayed in the browser, instead it's a XML page.
So, my question is, what do I need to do in order to make the Process Fields work with my form? and the user can submit the form by email too.
also, whatever changes I need to make, it won't break the Signatures.
thanks

Answer 1

Hi,
Regarding field transfer, I answered your previous post.
Regarding the project tree navigation, you can use function module 'BAPI_BUS2172_GET_TREE' (with the project guid as import parameter), and then sort the table Ascending or Descending.