#PB_Input_Eof is "\nEOF" in my 6.20 version on MacOS. I don't have another OS to test on.In non-graphical mode, a special return-value of #PB_Input_Eof (equals Chr(4)) will be received if the user enters a single Ctrl+D in the console, or a file that has been redirected to the programs input has reached its end.
Using <C-d> returns an empty string and then any later Input() returns #PB_Input_Eof.