OWA_UTIL.MIME_HEADER( 'text/html', false, 'UTF8' );
  HTP.p ('Content-length: ' || DBMS_LOB.getlength( p_str_blob ) );
  OWA_UTIL.http_header_close;

  WPG_DOCLOAD.download_file( p_str_blob );

declare
   p_str_clob clob;
   p_str_blob blob;

   dest_offset NUMBER :=  1 ;
   src_offset NUMBER :=  1 ;
   amount INTEGER := dbms_lob.lobmaxsize;
   blob_csid NUMBER := dbms_lob.default_csid;
   lang_ctx INTEGER := dbms_lob.default_lang_ctx;
   warning INTEGER;
begin
  select 'текст' 
  into p_str_clob 
  from dual;

  DBMS_LOB.CREATETEMPORARY(lob_loc=>p_str_blob, cache=>TRUE);
  DBMS_LOB.CONVERTTOBLOB( p_str_blob, p_str_clob, amount,dest_offset,src_offset,blob_csid,lang_ctx,warning );

  OWA_UTIL.MIME_HEADER( 'text/html', false, 'UTF8' );
  HTP.p ('Content-length: ' || DBMS_LOB.getlength( p_str_blob ) );
  OWA_UTIL.http_header_close;

  WPG_DOCLOAD.download_file( p_str_blob );
end;