Adding Web Parts to DispForm, EditForm, or NewForm
By default, you can not edit the standard form pages (DispForm, EditForm, NewForm). This is an annoyance if you want to add a Web Part to the page.
To be able to edit the page, go to the desired page, and edit the URL directly by removing everything after the id parameter and add "&PageView=Shared&ToolPaneView=2". Hit enter or Go, and it will place you into an edit mode for the page. Once you add a new web part, the page will always load with the option to edit the page.
Also, if you're editing the NewForm, there won't be an id of course, so just remove everything else after the ?, and add the new parameters.
Change the url from