I work in windows form 2015

when i need to read qr code i connect scanner to computer as USB

then open my windows form and put cursor in specific text box as textbox4

and it read success

so that

How to recieve data reading from scanner to textbox4 only and split data

if textbox 4 is hidden ?

private void textBox4_KeyDown(object sender, KeyEventArgs e)  

               string[] lines = textBox4.Text.Split(new string[] { Environment.NewLine }, StringSplitOptions.None);  

           if (lines.Length > 4)  
               textBox1.Text = lines[1].Substring(lines[1].IndexOf(":") + 1);  
               textBox2.Text = lines[2].Substring(lines[2].IndexOf(":") + 1);  
               textBox3.Text = lines[3].Substring(lines[3].IndexOf(":") + 1);  
               textBox5.Text = lines[4].Substring(lines[4].IndexOf(":") + 1);  

If the data is already in TextBox4 (that's what I think you are saying) then you can read/write the text whether or not the control is visible just like you would with any other control, but if it IS hidden then I don't see how the KeyDown event for TextBox4 is ever going to be triggered.