use 5.16.2;
use Win32::OLE;
use Win32::OLE::Const 'Microsoft Office 15.0 Object Library';

my $word = Win32::OLE->new( 'Word.Application', 'Quit' );
my $doc  = $word->Documents->Open( 'C:\Temp\OLE\Word\test.docx' ) || die 'Unable to open document: ', Win32::OLE->LastError;

my $paragraphs = Win32::OLE::Enum->new( $doc->Paragraphs );

while ( defined( my $paragraph = $paragraphs->Next ) ) {
    my $words = Win32::OLE::Enum->new( $paragraph->{Range}->{Words} );

    while ( defined( my $word = $words->Next ) ) {
        $word->{Text} =~ s/([Hh])i/$1ello/;
    }
}

$doc->Save;
$doc->Close;