Note:
When submitting data to a URL, it is recommended that you specify an absolute target. Relative targets are interpreted relative to the user environment, which can vary from one user to the next at run time.
This format submits a text stream to the specified Uniform Resource Locator (URL) by using the POST method. The text stream can be parsed by an FTP server, a mail server, a web server, or a CGI script that processes HTML forms. To use this method, users must open the form in Adobe Reader 6.0 or later or a web browser unless the URL specifies the mailto protocol.
See also 

To insert a submit button that sends a text stream using the POST method