I'm working on a upgrade from v9 to v10 and we have several custom aspx files that need to be migrated to v10.
How can we do it?
New MVC pages you need three things a model, a controller and a view (which is what MVC stands for).
An MVC example the visual studio newly created project is a decent starting point. https://docs.microsoft.com/en-us/aspnet/mvc/overview/getting-started/introduction/getting-started goes over creating such project fairly well. Hopefully that points you in the right direction.
Without any other detail it sounds like routing and/or controller and action names do not match up therefore causing a 404.
How can I create completely new MVC pages? Do you have an example?
I tried and I got .dll and .cshtml on the output, I moved them to the site. But when I went to the browser and tried go to a new page, I get a 404 Page Not Found (( I'm wondering what I'm doing wrong. Perhaps there are examples that I can look at.
I going to guess you want to have MVC pages and don't want to copy the .aspx pages over. Otherwise the aspx pages can be copyied over and still work with minimal tweaking. Just keep in mind the .aspx pages will have a different skin/theme files since the technology is different.
Speaking on just my experience on, there are two methods I have seen/done when it comes upgrading pages from asp.net web forms to MVC pages.
The 1st is to create completely new MVC pages. The advantage recreating is the code will of be created to work under MVC from the start.
The second is do a find and replace to create new files. In this case .aspx.designer.cs is used to make the Modal, .aspx.cs used to make the controllers and .aspx to create the view. This method is not perfect and will still require manual code changes/checks. This due to things like visibility being dedicated field in the modal instead of a control. The main advantage find and replace has is it can be easier to make sure logic is not lost and many pages get a soft conversion fairly early on compared to creating from scratch.
With both methods I highly suggest to get an understanding on how a ActionResult and routing work together in MVC if nothing else.
Hope listing some methods/options helps.