Close current form, open new form and return back to previous form

Note: Form1 stays hidden, but wasn't closed.

WinForm:

You can check if Form1 is already opened by using Application.OpenForms Property (System.Windows.Forms) | Microsoft Docs[^]

Form frm = Application.OpenForms["Form1"]; //it should works
frm.Show();

Note: please, read carefully Security section.

WPF:

There's a collection: Application.Current.Windows

Application.Current.Windows.OfType<Window>().Where(x => x.Name == "Form1").FirstOrDefault()

//try this...it should work just fine


//from Form1 -> Form2

this.hide();
Form2 form2=new Form2();
form2.Show();


//from Form2 -> Form1

this.hide();
Form1 form1=new Form1();
form1.Show();

to Do it right specilly if you set the MDIParent and if the first page is a Search Page.
as below

1- in the second form create Form variable
Form f;
2- then sent the veriable as below
internal void SetPrevForm(Form p)
{
f=p;
}
3- in the first form call it as below
in the Button click event do as below

Form2 f = new Form2()
f.SetPrevForm(this);
f.show();
this.hide();

4- in the close button at Form2
f.show();
this.dispose();