Microsoft Ultimate Word Games

This achievement definitely won't come naturally, so you'll have to make a point to do this at some point. The easiest puzzles to do this on are the first 15 puzzles on adventure maps from July 2017 onward. They are only 10x10 grids instead of the standard 15x15, so you'll only have 8-10 border entries to enter, plus these puzzles are incredibly easy.

As the achievement description says, you cannot enter a letter in any other box before finishing the outside answers. Make sure you're typing in the correct direction and don't accidentally enter your answer down instead of across, for example. Since you can't enter any other answers, if you need the help of crosses to figure out the border words, you could always solve on scrap paper or figure answers out in your head. As far as I'm aware, hints don't affect this achievement either, so you could use them to help figure out answers too.

Once you've got all the answers entered along the edges, you have to choose "check puzzle" to check them all. Once all the edge answers are green, if there are no other letters in the grid, the achievement will unlock.