Typo:
$word->run("vad", "D:\\Prasad\\Projects\\tools\\vad"');
should be
$word->run("vad", "D:\\Prasad\\Projects\\tools\\vad");

And:
#$word->run("vad")       #running fine
should be:
#$word->run("vad");       #running fine

A working example based on what you have

use strict;
use warnings;

use Win32::OLE;
use Win32::OLE qw(in with);
use Win32::OLE::Const 'Microsoft Word';
$Win32::OLE::Warn = 2; # Throw Errors, I'll catch them

my $word = Win32::OLE->GetActiveObject('Word.Application') || 
        Win32::OLE->new('Word.Application', 'Quit');    #get the word 
++object
$word->Documents->Add || die("Unable to create document ", Win32::OLE-
+>LastError());

$word->run("test", "D:\\Prasad\\Projects\\tools\\vdd");
[download]

With a word macro:

Sub test(teststring as String)

MsgBox(teststring)

End Sub
[download]

Works as expected

Update: Removed redundant br tag

Martin