error: Undefined variable: attr

I’ve installed the plugin. I have this line in a post:

[embed]https://dev3.sunil.co.nz/wp-content/uploads/2014/08/RJRabin_RESUME4.pdf[/embed]

The resulting page shows no pdf.
The following error message shows:

Notice: Undefined variable: attr in [prefix]/public_html/dev3/wp-content/plugins/dirtysuds-embed-pdf/embed.php on line 100

The line in question is from the file ’embed.php’, and looks like this:

return apply_filters( ’embed_pdf’, $embed, $matches, $attr, $url, $rawattr );

https://www.ads-software.com/plugins/dirtysuds-embed-pdf/