HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

Your Heroes3.exe 4.0 is not supposed to be seen by the HD mod, but the included Heroes32.exe (3.2) should work perfectly, which it does—at least with licensed (or copies of) Russian SoD and Complete, English SoD and Complete, GoG.com Complete, the Polish Gold Edition, and the Czech Complete.
If you need a fully standalone version in English (with all videos, not requiring a disc/image in the drive), you should look for Heroes of Might and Magic Complete (GoG) (GoG.com). Just not on GoG.com itself because you'd have to pay; get it from some torrents instead. If you need the Russian version, look for the Buka disc image.

Download it if you want, but in any case, I'm already pulling this Geedunk from torrents and will see what kind of thing it is.