How to maintain the focus of the dialogue, without losing the focus of the form?

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C#

VB

I am developing an application where I need to edit a Notepad file. I did the standard menus of the Notepad, and when some of them are clicked (Find, Find Next, Replace, Go To) they call dialogs that display textboxes and buttons to perform the selected task, such as Notepad.
When I click the Find menu, the Find dialog is called, it has the same buttons that the dialog Find of the Notepad. So when I type some text and click the Find Next button a routine that locates the text will be called, and found text will be selected in the text box containing the text of the Notepad in which I am using. I want that after the text was selected the dialog remains displayed, and when I click the Find Next button again, the next text to be selected without the dialog loses focus, and I can click on the text box, which contains the text of the Notepad. Just like the Windows Notepad.
I know two ways to call the dialog, the methods show () and ShowDialog (), but with none of them I can do what I want.
Does anyone know how I can do this, thank you in advance.