We can Read Out Protected MCU PIC18F4682 Internal Program, please view the Protected MCU PIC18F4682 features for your reference:

The minimum programming block is 4 words or 8 bytes. Word or byte programming is not supported. Table writes are used internally to load the holding registers needed to program the Flash memory. There are 8 holding registers used by the table writes for programming.

Since the Table Latch (TABLAT) is only a single byte, the TBLWT instruction may need to be executed 8 times for each programming operation. All of the table write operations will essentially be short writes because only the holding registers are written when Read Out Protected MCU PIC18F4682 Internal Program.

At the end of updating the 8 holding registers, the EECON1 register must be written to in order to start the programming operation with a long write. The long write is necessary for programming the internal Flash. Instruction execution is halted while in a long write cycle.

The long write will be terminated by the internal programming timer. The EEPROM on-chip timer controls the write time. The write/erase voltages are generated by an on-chip charge pump, rated to operate over the voltage range of the device if Read Out Protected MCU PIC18F4682 Internal Program.

The default value of the holding registers on device Resets and after write operations is FFh. A write of FFh to a holding register does not modify that byte. This means that individual bytes of program memory may be modified, provided that the change does not attempt to change any bit from a ‘0’ to a ‘1’. When modifying individual bytes, it is not necessary to load all 8 holding registers before executing a write operation before READ MCU.