First, a smooth surface is required. It has long been observed that two objects with smooth surfaces will adhere to each other—for example, two ultra-smooth glass plates. This is due to intermolecular forces, as a smooth surface maximizes the contact area between the two objects.
A surface that appears smooth to the naked eye is still uneven at the microscopic level, meaning the actual contact area between two objects is very small when they are in contact. However, if there is a layer of water on the surface—such as a thin film of water on a table—you will notice that a teacup seems to be "sucked" to the table. This happens because water fills in those microscopic grooves invisible to the naked eye, increasing the contact area between the teacup and the table, with atmospheric pressure also playing a role here.
To eliminate the influence of atmospheric pressure, take two flexible rigid PET plastic sheets, wet them to make them stick together, and then separate them horizontally from top to bottom. Under this condition, the atmospheric pressure on both the inner and outer sides of the sheets is equal. You will see the two plastic sheets separate in a Y-shape rather than a V-shape; the stress causing the deformation of the plastic sheets comes entirely from intermolecular forces, with the water acting as an adhesive in this case.
This demonstrates that the adhesive force of a binder stems from intermolecular forces.