acquia/solr/D7: indexing additional files outside of a node
Decided just to work within the Drupal framework rather than trying to hard-code something special. After I split the PDF, for each page I used file_save_data() to register the file in the file_managed table, then added the resulting file to the node in a separate file field:

$thisSplitURI = "{$splitURI}/{$finalFilename}_{$i}.pdf";
$thisSplitPath = drupal_realpath($thisSplitURI);
$file = file_save_data($contents, $thisSplitURI); // $contents is the value where the raw PDF contents are stored
$file-&gt;display = 1;
$node-&gt;field_split_pdf_pages[LANGUAGE_NONE][] = (array) $file;


Probably not ideal, especially when there's an 800-page document in there, but it gets the job done.