For the most reliable software and drivers, visit the official HP support pages specifically for the SCX-4521 series:
Given the age of the SCX-4521F (released circa 2006–2009), there may come a time when SmartThru 4 will not run on future versions of Windows. Here are three alternatives.
: The primary portal for downloading drivers and scanning software.
If the software is no longer available on the official site (common for older hardware discontinued before the HP acquisition), you may need to use reputable driver archive sites. Use these with caution and ensure you have active antivirus software when downloading from third-party sources.
Basic tools to crop or adjust scans before saving. Installation Tips for Modern Windows