@reports = `ls *.doc`;
foreach $file(@reports) {
$cmd=`perl -ni -e 'print;print "VALUE=KEY\n" if \$\.== 3;' $file`
}
[download]

The above code is working fine now, with this i can able to add a line to around 1400 report files.

That script will be creating ~1400 perl processes. You've been repeatedly advised about this yet you continue to do it.

This script performs exactly the same function but only uses one perl process:

#!/usr/bin/env perl -i

use strict;
use warnings;

while (<>) {
    print;
    print "VALUE=KEY\n" if $. == 3;
    $. = 0 if eof;
}
[download]

I suggest you read "perlrun - how to execute the Perl interpreter". Amongst other things, this will tell you about the Command Switches: perhaps lack of knowledge in this area is why you're coding your script the way you are.

I put the above code in pm_1076103.pl and created three *.doc files:

$ ls -al *.doc
-rw-r--r--  1 ken  staff  52 26 Feb 03:20 pm_1076103_1.doc
-rw-r--r--  1 ken  staff  52 26 Feb 03:22 pm_1076103_2.doc
-rw-r--r--  1 ken  staff  52 26 Feb 03:22 pm_1076103_3.doc

$ cat pm_1076103_1.doc
Doc 1 Line 1
Doc 1 Line 2
Doc 1 Line 3
Doc 1 Line 4

$ cat pm_1076103_2.doc
Doc 2 Line 1
Doc 2 Line 2
Doc 2 Line 3
Doc 2 Line 4

$ cat pm_1076103_3.doc
Doc 3 Line 1
Doc 3 Line 2
Doc 3 Line 3
Doc 3 Line 4
[download]

I then ran the script like this:

$ pm_1076103.pl *.doc
[download]

Here's what the *.doc files now look like:

$ cat pm_1076103_1.doc
Doc 1 Line 1
Doc 1 Line 2
Doc 1 Line 3
VALUE=KEY
Doc 1 Line 4

$ cat pm_1076103_2.doc
Doc 2 Line 1
Doc 2 Line 2
Doc 2 Line 3
VALUE=KEY
Doc 2 Line 4

$ cat pm_1076103_3.doc
Doc 3 Line 1
Doc 3 Line 2
Doc 3 Line 3
VALUE=KEY
Doc 3 Line 4
[download]