custom php in action url of a form

Hi,

I have created a page in wordpress which has a form.
What this form does is, takes input as a paragraph and passes it to other php file specified in the action attribute which provides some
formatting and indentation to the input and displays it to user for
him to copy.

Now i have created a custom page template for the page containing the
form for adding some customization to this page only.

I have kept the php file in ” wp-content/themes/theme_name “
and set the action url as “www.blog_name.com/wp-content/themes/theme_name/formatter.php”
AND
“www.blog_name.com/formatter.php”
but it doesn’t work.

Here i don’t know, what to put in the action attribute. And also
where my other php file should go.

Somebody suggested to keep the form and other php code which does all the formatting in the page template itself which i have created to customize earlier.

I’m very much confused here. Please help.