StuffIt Deluxe 16 may not run natively on newer macOS versions (Catalina or later, which require 64-bit apps). It was primarily designed for older Mac systems.

Official serial numbers for StuffIt Deluxe 16 are typically unique to the individual purchase and follow a specific format.

StuffIt Deluxe 16 was designed for older versions of OS X. Running an unpatched, cracked version on a modern macOS environment can result in immediate application crashes, kernel panics, or corrupted file compression, potentially destroying important archives. Modern, Free Alternatives for macOS

StuffIt Deluxe was once the industry standard for file compression and expansion on the Mac platform. Developed originally by Aladdin Systems (and later acquired by Smith Micro), the ".sit" and ".sitx" formats were ubiquitous in the 1990s and 2000s.

: StuffIt Deluxe registration numbers usually begin with the prefix DLX , while the Standard version uses DRP . Compatibility & Technical Requirements

What are you trying to open (e.g., .sit, .zip, .rar)? What version of macOS is your computer currently running?