A DLL file, short for Dynamic Link Library, is a sort of file that contains codes and instructions that can be used by more than one program simultaneously. It means that multiple applications can share the data that is contained within a single file. DLL files are responsible for the proper functionality of Windows operating system and applications within it. Thus, it is imperative to maintain these files clean.
The DLL file was implemented in order to reduce the memory usage on the operating system. Multiple processes that load the same DLL file share a single copy of the file in the physical memory; thus saving memory and improving overall performance of your system. Furthermore, programs written in different programming languages can use the functions written in a DLL file.
If by any chance the DLL file turned out to be corrupted or missing it could lead to failure of a certain application or even worse, the whole Windows operating system. It is so because DLL files tend to require other DLL files to function properly. Third-party application may also use the system DLLs. For example, your video drivers may be calling upon the Windows DLL files to startup at the same time as Windows do, etc. The importance of DLL file to your system is irrefutable.
Some malware is capable of inserting certain DLL files of its own within the system, or it could replace the already existing ones. It could be the reason one or more applications on your PC are not functioning properly. The most important thing here is to understand that simple removal of DLL file will not work, and in fact, it could lead to total failure of a certain program or Windows system in general. That is because the program might be still trying to call upon the deleted DLL file. In order to delete DLL file your must unregister it first, meaning that a certain application will not be calling on it anymore. After a successful unregister process, it is safe to delete the malicious DLL file from your operating system.