The document explains dynamic link libraries (DLLs), which are collections of small programs that executables can call upon when needed to enhance functionality without expanding file size. It warns against downloading DLLs from unapproved sites, as these may be outdated, infected with viruses, or only partially solve underlying software issues. The document emphasizes that troubleshooting the root cause of problems is crucial rather than simply replacing missing DLLs from unreliable sources.