Pretty Permalinks with Form Data Submission

Hello,
I have a form which manipulates data from form fields.Everything is inside a PHP script and I use POST to send data to itself.
Now, I am trying to integrate it with Thematic and so created a new Page Template and added all PHP Codes after the contents.

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So,it works without pretty permalink and returns the PHP results back to the page.But I cannot figure out the form to work on Pretty Permalinks like example.com/test .Same configuration gives 404 Error and typing the whole https://example.com/?page_id=8 don’t work too.