Receiving an "Unknown Format" error code when submitting a form

Question

Product: Adobe Acrobat 9 Pro Extended
Hi, I'm trying to find out what exactly is Acrobat expecting as a return value on its form submission.
two parts to my setup:
1. The form. It is a garden vaiety form with a button on it which set up as follows:
Action -> Mouse Up -> Submit a form -> PDF The complete document
2. The receiver.  This is a REST based service, expecting a HTTP Post.
For the most part, the whole setup works like a charm - the form is posted by the client, the server receives the file, creates a local copy and processes it correctly. After the post is successfully received, the last step on server is to send a reply to the client. This is where I’m getting stuck.
If I return an HttpStatusCode.Ok and a blank SOAP.Fault, I’m getting and “Unknown Format” error on the client side. I tried several different combinations/values/etc, including sending the result code only, but since I don’t know what exactly is acrobat expecting, I’m just shooting in the dark. Other error codes I’ve seen include “Invalid Server Response”.
Unfortunately I can’t find any guidance from Adobe on what Acrobat is expecting in return for the submit functionality, so any help/pointers are greatly appreciated.
Thanks everyone!

Answer 1

Here is the contents of a sample FDF that will cause a popup to display when it is imported:
%FDF-1.2
1 0 obj
<< /FDF << /Status (Your message goes here.) >> >>
endobj
trailer
<< /Root 1 0 R >>
%%EOF
Replace "Your message goes here." with the text you want to display, and don't change anything else in the sample. The value of the /Status key in the FDF is a PDF string, so it has to follow the rules described in the PDF standard (ISO 32000) for strings. So read up on it so you know how to properly escape/encode PDF strings.
Note that the server needs to set the MIME type of the response in the "Content-type" HTTP header to "application/vnd.fdf".