here is solution, which help me, combining all of your answers, I know name of start Paragraph, but don't know name of end Paragraph, so...THANKS (sorry for mess in replies):

#!perl

use strict;
use warnings;
my $para = 'Paragraph2:';

while (<DATA>) {
    print if (/^ {5}$para:?\s*$/i ... /^ {5}\S/ and /^ {7}/) 
}

__DATA__
     Paragraph1: 
         text11
     Paragraph2:
         text21
         text22
         text23
     Paragraph3:
         text31
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