What is the maximum document length the DR-C125 can scan, and how do I enable it?

The scanner can scan documents up to 3,000 mm (118.1") long when set to Long Document mode; the standard maximum length is 356 mm (14"). On Windows, enable this through the Canon imageFORMULA Utility by clicking Properties, then the Maintenance tab, and selecting either Long Document mode (1,000 mm) or Long Document mode (3,000 mm). When using Long Document mode, always set the feed selection lever to the non-separation position and scan documents one at a time. (Page 32-33)