Remove all the parenthesis from $startstring, $keywords and $endstring, and write:

@finds = $data =~ m/(?:$keywords)\s*.{0,1500}\s*$startstring(.*?)$ends
+tring/gis;
[download]

But do note that if your text is:

Security Ownership bla bla
<table>Foo bar</table>
more than 5%
<table>Text text</table>
All Directors and Executive Officers
<table>Even more text</table>
[download]

@finds will only get one entry: "Even more text", due to the greediness of .{0,1500}.