I have an Umbraco Document Type and a template with the same name. I create a page in Umbraco and can view the page with the details entered. On this page i now would like to build a form so it can be submitted. As soon as i declare the model in the top of my cshtml file, i get an error about the ViewData (ViewDataDictionary) is of type X but this method requires Y. How am i supposed to set this up so both the content from Umbraco work and my custom form would work?

Out of my head, but you can use the UmbracoViewPage model for

If you're building a form - you probably want a surface controller https://docs.umbraco.com/umbraco-cms/reference/routing/surface-controllers/ This is probably a good start https://codeshare.co.uk/blog/how-to-create-a-contact-form-in-umbraco-using-mvc-and-c/