adc.exe belongs to Active desktop calendar from XemiComputers. This application allows an interactive calendar to be displayed on the desktop and also features notes, and reminders. This is a non-essential process.
Disabling or enabling it is down to user preference.
Non-system processes like adc.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that over time your registry suffers fragmentation and accumulates invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues