What kind of file is it, actually? Smells like a csv file with multiline fields, in which those lines are separated by ^M. In any case, that smells like an XY problem.

There's no such thing as a DOS line feed - a line feed is "\n" or ASCII 10. Carriage return is "\r" or ^M or ASCII 13. DOS line endings are "\r\n" (or CRLF). Establish what is your line ending proper (possibly "\r\n"), read the lines setting $/ to that line ending (see perlvar), then convert any (multiple) "\r" occurrences as per the specs of the task (which are those?). A few sample lines would be helpful for further advice.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}