Earlier it was giving you error. Try this. I have fixed errors in PHP syntax.
function as_pdf_link( $strContent ){
global $wp_query;
$strHtml="
<div id="aspdf">
<a target="_new" href="" . get_bloginfo('wpurl') . '/wp-content/plugins/as-pdf/generate.php?post=" . $wp_query->post->ID . "" onclick="open(this.href, this.target, \'width=600, height=450, top=200, left=250\'); return false;">
<span>' . stripslashes( get_option( 'as_pdf_linktext' ) ) . '</span>
</a>
</div>
';
return $strContent . $strHtml;
}