A family of Microsoft word processing software products for creating web, email, and print documents.
Microsoft's justification algorithm is crummy. As you've noted, it only adds spaces between word, not between letters.
Here's a macro you can run that will put the document into Word 2010 compatibility mode, then apply WordPerfect-style justification, which adds space between letters as well:
Sub ApplyWPJustify()
With ActiveDocument
.SetCompatibilityMode wdWord2010
.Compatibility(wdWPJustification) = True
End With
End Sub
Please note, after you run this, if the document is upsaved to a current Word version, the justification will revert to the standard poor spacing.
Or use left-aligned text, which has been shown to be more readable that justified text.