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You can do this similarly to how you would add nailhead trim to upholstery, but you should avoid kinds installed with nails. Instead, use trim with adhesive backing that can be pressed into place along the bare edges of MDF. MDF is a pretty resilient wood and, in many cases, it will cause nails to bend as they’re pounded in. If you absolutely must use nails on MDF, use a nail gun. bare MDF. Choose a color that complements your home color scheme or the content of the poster. When in doubt, black is a simple, elegant color that goes with most kinds of decor. Consider painting before you mount your poster to prevent paint from getting on the poster. This is the most common style for a plaque mount. Beveled edges will give your MDF a professionally finished appearance and make it even more prominent.

Summary:
Add nailhead trim around the bare edges of the MDF mounting. Paint Bevel the edges of the MDF mounting like crown molding.