Yes, but with nuance. If the copyright has expired (generally 70 years after the author's death—Dvorak passed in 2020, so his works are still protected in most jurisdictions) or if you own a physical copy and download a digital backup, it is generally considered fair use. However, many free PDFs circulating on file-sharing sites are unauthorized copies.
So why should you use Milan Dvorak's Jazz Etudes in your practice routine? Here are just a few of the benefits: milan dvorak jazz etudes pdf