define new section, like the_content, the_title for a custom form

I want to define a new section, like the_content. It’s for a custom form. No filters are being applied to the form that I’m using. The plugin that I’m using applies filters to certain sections, like the_content. Do custom (non-wordpress) forms have a default value? I need to know how to do this so that the filters in the plugin can be applied to my own form.