LibreOffice is outstanding. I've used it since 1999 when it was Star Office. You can write anything and export to PDF easily. You can also share your work with MS Office users. Writing business letters is a simple discipline. Content and simplicity go hand in hand. LibreOffice will also work for you on Windows or Linux. Finally anyone who claims LibreOffice is dated probably doesn't know that humans have been writing for 4 thousand years and we have never had it so good as we do now!