@manahilsami
you're question is a bit confusing. There are three potential questions I think you MAY be asking here:
How to embed a Marketo form on a non Marketo page
Are you asking how to embed a Marketo form on a non Marketo page?
If so, embedding a form on any page is pretty easy


- Click Here
- Click Here
- Copy the embed code and place it on your page.
This won't support prefill, so you probably want to then look at this more complex, but brilliant approach by the legend that is @sanfordwhiteman : https://blog.teknkl.com/pre-fill-any-site-any-form/
Form based Smart Campaign triggers and filters
If you're asking how to tell if a marketo form has been filled out - it is irrelevant as to which site the Marketo form is on.. the standard triggers and filters will work just fine.


How to capture data from a NON Marketo form
If you're not using a Marketo form to capture the data you need a slightly different approach.
In that instance, the approach is to load the Marketo form in a hidden div.
On the submit of your visible form, you need to populate all the fields on the Marketo form, and then trigger a submit of the Marketo form.
If you need more detail on this, let me know.
Finally
You may be asking a totally different question, in which case can you elaborate a bit further please.
Cheers
Jo