In blue prim, to save the note pad file we are passing global send keys "^s". After that in order to write the File name we use a navigation stage. Now my question is why we are not using write stage to give the note pad file name?
You're right - there are multiple ways to write a text. You can use write section, sendkeys, "set clipboard" or you can just write a text file using code stage. In work, you can probably can use anything you want, if it's stable and does the thing right.
I assume, you're doing some exercises, so you're probably asked to do it in a way to learn one method of doing this thing.