Is it permissible to promote oneself by mentioning good qualities and concealing shortcomings when applying for a job, and is that considered a sin?

Originally, self-praise is blameworthy, but it is permissible in cases of necessity and benefit, such as mentioning qualifications for a job, provided one is truthful, as Allah Almighty says: (O you who have believed, be persistently Qawwameen [upright] in justice, witnesses for Allah, even if it be against yourselves or parents and relatives.) An-Nisa/135.

As for concealing negatives and shortcomings: - If they are not related to the work, there is no harm in concealing them. - If they are related to the work and affect it, then it is obligatory to disclose them and not conceal them. They can be mentioned along with a commitment to address and overcome them.