What is the best way to protect hex file from being read from a Microcontroller?

Each microcontroller provides a lockbit that wil be specified in the datasheet. This lock bit is responsible for protecting anyone from readig the hex file from the microcontroller depending on whether its set or not. Setting the bit is done i the user program. There are other devices called one time programmable devices which are the best interms of hex file protection as compared to reprogrammable devices

by using a lock code we can protect hex file

Every microcontroller datasheet is provided with lock bit inormation which can be enabled in program code, this will allow to protect code against copying. One of the best way to protect code from being copied is using OPT (One Time Programmabe) devices as any reprogrammable microcontroller is vulnerable to code copying issues. 

applying security procedure .its depends upon the software ,which are using for making hex file programes

it depends on the program which uses for programming microcontroller

We can Protect the HEX file by enabling lock bits.

Break the pins utilized for programming after burning your program and don't utilize that pin in your codes this is the simplest way to protect your HEX file.

cant protect HEX file from microcontroller.

Read a Device and Save the Hex File

Don't utilize the pin in your codes this is the simplest way to protect your HEX file.