Not quite sure what this is needed for, but the following seems to meet your requirements well enough.

#!/usr/bin/perl

use warnings;
use strict;

my $test = 'doc123/print doc456/read doc789/print doc145/print doc123/
+read';
my %count;

print join '/',
  grep {s/^([a-z]+)\s/"$1".(++$count{$1}).' '/ie || $_}
  split '/',
  $test;
[download]