There are a number of commercial editors for EDIFACT messages. A free editor is also sufficient.

Notepad++ has proved its worth. This makes it easy to insert a line break after the segment separator to make the file easier to read.

In this case, it is preferable to record a macro inside Notepad++ that performs the search and replace of the quotation mark with quotation mark and line-switching to keyboard shortcuts.

In the FAQ How to highlight EDIFACT segments? in color is also mentioned how to highlight EDIFACT segments in color.

For reading Edifact files, you can use the free editor Notepad++.

It supports the creation of your own language definitions.

We did this for Edifact and provide this language definition file.