how to change font family of all control on window form using c#

For an alternative to the usual, let's grab all the Controls using a Stack ... not doing recursion in the usual manner:

using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;

public static class SpecialMethods
{
    public static IEnumerable<Control> GetAllControls(Control aControl)
    {
        Stack<Control> stack = new Stack<Control>();

        stack.Push(aControl);

        while (stack.Any())
        {
            var nextControl = stack.Pop();

            foreach (Control childControl in nextControl.Controls)
            {
                stack.Push(childControl);
            }

            yield return nextControl;
        }
    }
}

If we wanted to set a specific Font for all Controls on a Form, we could use something like this in the Load Event of a Form:

Font theFont = new Font("Arial", 9.0F, FontStyle.Bold);

foreach(Control theControl in (SpecialMethods.GetAllControls(this)))
{
    theControl.Font = theFont;
}

If we wanted to set only the Font of Button Controls:

foreach(Control theControl in (SpecialMethods.GetAllControls(this)).OfType<Button>().ToList())
{
    theControl.Font = theFont;
}

Make sure the Form references Linq.

Sources: this post, in 2009, on StackOverFlow alerted me to the possibilities of using a Stack to make recursive traverses in .NET more efficient: [^].

Be sure and see mrydengren's response: [^], and Eric Lippert's response: [^].

Here is one solution:
check here[^]