SOLR Snippet with link to PDF
you can add extra field to solr.
you need to implement
hook_apachesolr_index_document_build_node(ApacheSolrDocument $document, $node, $env_id) 

and there $document->addField('pdf_field_name', 'your_url');

also you need to implement hook_apachesolr_query_prepare(DrupalSolrQueryInterface $query) 

and add there $query->addParam('fl', 'pdf_field_name');

then in your search-result.tpl.php 
$pdf_field_name should be available (after reindexing)