How to write a reply rejection letter to candidate who apply to our company?

You should have a standard letter you send to any job applicant that says, "We have reviewed your resume and at the present time we do not have any openings that match your job skills and experience."

That is ALL you should say in the letter. You should not say you're sorry, you should not discuss any jobs and you should never, ever say you will keep the resume on file. Keeping old resumes on file can result in serious legal problems if at some time in the future you hire someone for a position who is less qualified than someone who's resume you have on file and forgot to review.

You should also write a company policy that stipulates you only accept resumes for open positions that have been publicly advertised. That way whenever you receive a resume for no specific reason, you can respond simply that "We only accept resumes for positions that have been publicly advertised."