There are a few ways to create a fixed-width file, depending on your operating system and the tools you have available.
If you're on Windows, you can use the built-in Notepad application to create a fixed-width file. Just open Notepad and enter your text. Then, go to the File menu and choose Save As. In the Save As dialog box, select the All Files (.) option in the "Save as type" drop-down menu. Enter a name for your file and append the .txt extension to it (for example, fixed-width.txt). Finally, click the Save button.
If you're on MacOS, you can use the TextEdit application to create a fixed-width file. Just open TextEdit and enter your text. Then, go to the Format menu and choose Make Plain Text. Enter a name for your file and append the .txt extension to it (for example, fixed-width.txt). Finally, click the Save button.
If you're on Linux, you can use the nano text editor to create a fixed-width file. Just open a terminal window and type nano followed by the name of the file you want to create (for example, nano fixed-width.txt). Enter your text and then press Ctrl+O to save the file. Press Enter to confirm the file name, and then Ctrl+X to exit nano.