You'll need to scratch up the inside of the hoof where it's smooth in order to glue it down; use an industrial glue (like shoe goop or E6000) and then use weight and wait overnight for the glue to fully set.
Just keep in mind that foam -will- yellow with UV exposure over time, so lighter colors (like white or bone) could yellow over time, much like upholstery foams. So those are best covered. If you choose to get a colored version and don't want to cover them, there will be a color swirling effect due to the matte finish. It's also not unheard of for there to be some small bubbles here and there on the surface.
These are good for both indoor and outdoor use, and will not crack/break like resin hooves will.
Extra accessories to go along with these:
Small Rubber Horse Shoes