When to use first person and third person in writing a letter?

[alejandrobarts]

Good day teachers! I would like to ask when to use first person or third person in writing a letter. Can it be mixed?
1. The undersigned requests that he be granted five days leave. He will make use of the leave to move house.
2. The undersigned requests that I be granted five days leave. I will make use of the leave to move house.

 

[probus]

The first is grammatically correct and the second is not. But both are stilted and unnatural. Simple and natural is better. For example: I hereby request five days leave. I need this time to move house.