What does "Not enough space on drive C" mean?
DVDFab DVD Copy option needs at least 20 GB of Free Hard Disk Space.
Before the content of the movie is burned into the blank disk, DVDFab must finish certain decoding and encoding jobs which require some amount of free space on the hard drive to store data. 20 GB free hard disk space mentioned here is just for this issue. You can set the output directory and temporay directory to other drives which have enough free place in "General" settings window.
Can I copy entire movie to hard drive as only one VOB file?
DVDFab DVD Copy can copy the full movie from original DVD disc off onto your computer HDD as standard DVD movie folder, which has a "Video_TS" sub-folder in it. Inside this "Video_TS" sub-folder are several or lots of VOB files. DVDFab does break the file structures of the DVD, let alone merging the VOB files into one single VOB file.
Tip: DVDFab DVD Ripper has a ripping mode called VOB, its "VOB.passthrough" profile converts the entire main movie title to one single VOB file. You may give that a try.