Run steam://rungameid/4000
FileCreateDir, C:\Demos\

ErrorCount := MoveFilesAndFolders("C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod\demos\*.dem", "C:\Demos\")
if ErrorCount <> 0
    MsgBox %ErrorCount% files/folders could not be moved.

MoveFilesAndFolders(SourcePattern, DestinationFolder, DoOverwrite = false)
{
    if DoOverwrite = 1
        DoOverwrite = 2
    FileMove, %SourcePattern%, %DestinationFolder%, %DoOverwrite%
    ErrorCount := ErrorLevel
    return ErrorCount
}