Unity- after gathering letters in the game how can we generate random words at the ed of the level

I have a problem. -_- I am currently doing a little 2D children_game project in Unity where the idea is for the character to collect letters on the map, and at the end of the level, the collected letters to form a random word. I was thinking that this might be done through a text doc. with words, from which the letters to generate the word at the end. I am not quite sure if this is how it's going to happen or there is a different option for this.

Do you have an idea of how this can happen and how can be generated the word with the possible largest amount of letters (one of the longest possible words in the existing ones), because after a few levels the players will have to create a meaningful sentence, which will give them points?