A confirmation letter includes the salary, joining date, confirmation date, designation and job description of an employee. Later, if the employee moves to another company this letter acts as proof of the position n salary he held in his previous job.
When adding your salary to your cover letter, it's best to provide a range instead of a fixed number. Adding a desired salary range does not give your employer a specific figure. It does, however, provide them with a baseline expectation and some wiggle room for negotiation.