Print Distributor has a separate service component that runs independently from the management tool, this service can run in one of two different modes.
On Windows 7, 8 and 10 Print Distributor runs in the foreground, it starts when you sign in to Windows and stops when you sign out. While it is running you will be able to see the Print Distributor icon in the notification area on the toolbar.
Because Print Distributor is running under a standard user account it will be able to use mapped drives and connected printers associated with the account you have signed in under.
On Windows Server 2008, 2012 and 2016 Print Distributor runs as a Windows service, it starts when Windows starts and stops when Windows shuts down. This means it can process print jobs without a user being logged in which is what you would expect on a server.
By default Print Distributor runs under the System account which means if you want to access resources located on another machine you will need to use a UNC path (\ServerName\ShareName) and add your actions as children to a Run As action.
The Service menu in Print Distributor allows you to switch between the two modes so if necessary you can run as a Windows service on a client machine or in the foreground on a server. The later is useful if you are trying to debug issues with calling external programs with the Run Program action. The service menu also allows you to stop and start the service.
The status bar in Print Distributor tells you whether Print Distributor is running the foreground service or Windows service. It also tells you whether the service is running or stopped. If the service is stopped print jobs will block in the virtual printers.