How to disable textbox from editing?

You can set the ReadOnly property to true.

Quoth the link:

When this property is set to true, the contents of the control cannot be changed by the user at runtime. With this property set to true, you can still set the value of the Text property in code. You can use this feature instead of disabling the control with the Enabled property to allow the contents to be copied and ToolTips to be shown.

As mentioned above, you can change the property of the textbox "Read Only" to "True" from the properties window.

The TextBox has a property called ReadOnly. If you set that property to true then the TextBox will still be able to scroll but the user wont be able to change the value.