Old thread, but just in case anyone happens to stumble against this thread as I did, here is an addition that might be useful.

RTF specs admit non-ansi Unicode characters, by escaping them in decimal format. So in case your string has some non-ansi characters, you will also need to convert them to escaped. Fortunately, Encode can do it for you. Here is an example:

use Modern::Perl;
use utf8;
use Encode;

my $text = "Gen 1:1 Ἐν ἀρχῇ ἐ&#
+960;οίησεν ὁ θεὸ
+ς τὸν οὐρανὸ&#95
+7; καὶ τὴν γῆν.";

$text = encode('cp1253', $text, sub{ sprintf "\\u%d\?", shift }); # cp
+1253 is for Greek)
$text =~ s/([\x00-\x1F\x7F-\xFF])/"\\'" .(unpack("H2",$1))/eg;

say $text;
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Output will be: