Indexing pdf documents with indextype ctxsys.context

Question

I have an application that stores the contents of uploaded documents in BLOB data fields. We provide web pages which search through the uploaded documents based on text entered by the user. We currently upload both MS Word .doc and HTML documents. For the HTML documents, which are made available to the public, we index the table with the following procedure:
CREATE OR REPLACE procedure WEBADMIN.index_redacted_docs is
begin
declare
cur           PLS_INTEGER;
exec_int           PLS_INTEGER;
counter          number;
begin
select count(*) into counter
from user_indexes
where index_name = 'DOCS_CTX_REDACTED_IDX';
if (counter = 1) then
ctx_ddl.sync_index (idx_name => 'docs_ctx_redacted_idx');
else
cur := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE (cur, 'create index docs_ctx_redacted_idx on documents_ctx_redacted (blob_content) ' ||
     'indextype is ctxsys.context parameters (''filter ctxsys.null_filter'')', DBMS_SQL.NATIVE);
exec_int := DBMS_SQL.EXECUTE (cur);
DBMS_SQL.CLOSE_CURSOR (cur);
end if;
exception
when others then
     DBMS_SQL.CLOSE_CURSOR (cur);
     raise;
end;
end;
We run this process after every uploaded HTML file and are able to locate documents which contain any text entered by the user. The portion of the command we use to query the documents_ctx_redacted table (blob_content is the BLOB field in this table) is (using "corn" as a sample query text):
WHERE (contains (BLOB_CONTENT, 'corn', 10) > 0)
Our customer is now asking that PDF files be uploaded as well and searched in the same manner. After the PDF files are uploaded (into the same table as the HTML files) and the index updated, with the above command ctx_ddl.sync_index (idx_name => 'docs_ctx_redacted_idx'), since the index already exists, we cannot get any rows returned with the above WHERE (contains .... ) clause. We know the text we're looking for (such as "corn") is contained in the PDF files, but the search does not find them, although it finds the HTML documents just fine. I've also tried dropping the index entirely and recreating it, but that also only finds the HTML documents but not the PDF's.
What are we doing incorrectly with the PDF files? Thanks.

Answer 1

We are using Oracle version 10.2 . I looked at the relevant Oracle Text documentation for that version, and the best I could glean was that PDF files are supported by the filter ctxsys.auto_filter (rather than null_filter) when creating the index. I dropped the existing null_filter index and created a new index with the auto_filter parameter, but the end result was the same. I still get no PDF records found when issuing the command (using "corn" as the text query)
WHERE (contains (BLOB_CONTENT, 'corn', 10) > 0)
although the HTML records show up fine again.