PDF Plugin not parsing embeds

I’m experimenting creating a ‘PDF Version’ plugin using TCPDF. When I try grab the $TMPL->tagdata, it’s not parsing the embedded templates -just displaying the actual {embed="x"} tags in the resulting pdf. Here’s what I’m trying:

{exp:pdf_version}
   {exp:weblog:category_heading weblog="links"  parse="inward"}
      <h1>{category_name}</h1>
      {category_description}

      {embed="includes/.display_collection" collection="{collection}"}
      {embed="includes/.display_subcats" mycat="{category_id}"}

   {/exp:weblog:category_heading}
{/exp:pdf_version}

I’m very new to plugins, but I assume it’s a parse order issue? I tried setting PHP parsing to input and output with the same result.

Any help would be really appreciated. Thanks!