If you mean a (like Chegg, Course Hero, or a professor-provided key)— yes, use it wisely.

Invest your time in drawing clean free-body diagrams, practicing vector math, and forming study groups. A PDF can open doors, but only your own effort will carry you through to the final exam.

If by “solution manual pdf” you mean an from a torrent site— no, you should not download it. Not only is it copyright infringement, but it also puts you at academic risk. Many universities now use plagiarism detection software that cross-references solution manual phrasing.