help needed on INSTR

Hi,

I am using INSTR command to search within a blob for certain words. I am not able search within a pdf and also formatted word files. Does anyone have any idea?

I am using the following code :

SELECT LD_LETTER_NO FROM PRM_LETTER_DOCUMENTS
WHERE DBMS_LOB.INSTR( LD_DOC, RAWTOHEX( UTL_RAW.CAST_TO_RAW( 'search string' ) ), 1, 1) > 0

Here LD_DOC is the blob present in the database.

Any pointers for the same would be helpful.

Thanks,
Anju