You haven't shown any of your preexisting code, so I'll just assume that the whole document is in a single scalar already. Then you can simply a regular expression:

my $string = <<STATEMENT;
Wal-mart talks about its Significant Accounting Policies in its 10k.

Significant Accounting Policies are important for a firm.

Here is a list of the Significant Accounting Policies </b>

1)Lifo

2)Depreciation

3)Expenses
STATEMENT
if( $string =~ m/(.*)Significant\s+Accounting\s+Policies\b(.*)$/m ) {
    print "Found stuff: $2\n";
} else {
    print "Match failed\n";
};
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This relies on the first .* group being greedy and gobbling up as much as possible from the string, thus leaving only the last Significant Accounting Policies instance for the match.