Error - ORA-22835: Buffer too small for CLOB to CHAR or BLOB to RAW conversion (BLOB File to CLOB Variable Conversion)

Read a BLOB File the message and display the message into a variable.

Error - ORA-22835: Buffer too small for CLOB to CHAR or BLOB to RAW conversion (actual: 9923, maximum: 2000)

You can get around the buffer issue by reading the BLOB value in chunks. In order to do that, you can define a user defined function (UDF). The following UDF reads the BLOB field one chunk at a time, converts that to VARCHAR2 and appends the results consecutively to return the result as a CLOB:

CREATE OR REPLACE FUNCTION VARCHAR2CLOB_FROM_BLOB(B BLOB)
RETURN CLOB IS
    c CLOB;
    n NUMBER;
BEGIN
    IF (b IS NULL) THEN 
        RETURN NULL;
    END IF;
    IF (LENGTH(b) = 0) THEN
        RETURN EMPTY_CLOB();
    END IF;
    DBMS_LOB.CREATETEMPORARY(c, TRUE);
    n := 1;
    WHILE (n + 32767 <= LENGTH(b)) LOOP
        DBMS_LOB.WRITEAPPEND(c, 32767, UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.SUBSTR(b, 32767, n)));
        n := n + 32767;
    END LOOP;
    DBMS_LOB.WRITEAPPEND(c, LENGTH(b) - n + 1, UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.SUBSTR(b, LENGTH(b) - n + 1, n)));
    RETURN c;
END;
/