Is it considered a forgery if an applicant for a Civil Defense job is registered as medically fit despite having high blood pressure, and after donating blood the result did not change, then the result later became normal? And would the salary be permissible in this case?

The employee exceeded the limits by not changing the blood or reducing its quantity, because no bribe was offered to him, and there is no connection between you. So there is no blame on you, God willing, especially since you were tested a second time and the result was sound. If you are qualified for the job and can perform its duties, then there is no sin upon you in engaging in it and benefiting from its salary.