Does Passing Contact Information send hidden fields to TY page URL?

I want to pass a value from a hidden custom field captured on an optin page to the thank you page, using a Web Address thank you page with the ‘Redirect to thank-you page’ option selected.

If I check the box to ‘Pass contact’s information to the thank-you page,’ will it pass the hidden field value as a query parameter in the URL, or just the name/email/contact id values?

@John_Grimshaw,

My understanding is you have a form with at least one hidden field and that you have both the ‘Redirect to thank-you page’ and ‘Pass contact’s information to the thank-you page’ options checked, with a custom URL for The Thank-you page, similar to the example in the screenshots below:

Hidden Field Location on Form:

Thank You Page Settings:

I can confirm hidden custom field values will be passed to the thank-you page as parameters in the URL, in addition to the parameters you mentioned.

I am using plain html version of form which has some custom fields like
<input id="_sc" name="inf_custom_sc" type="hidden" value="test value">

this works only if I define this field on form builder first.

@John_Grimshaw Is it possible to add custom field dynamically from html form side or we need to define it from form builder first then use it.

<input id="_sc" name="inf_custom_sc" type="hidden" value="test value">
<input id="_bc" name="inf_custom_bc" type="hidden" value="bc value">

I have a lot of form already so dont want to edit all of them to add some fields