Brother MFC 9840CDW - Manual (Page 195)

ControlCenter2
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10
Scan to Image
10
General tab
Enter a name in Name for Custom (up to 30 characters) to create the button name.
Choose the type of scan from the Scan Action field.
Settings tab
Choose the Target Application, File Type, Resolution, Scan Type, Document Size, Duplex
(two-sided) Scanning (if necessary), Brightness and Contrast settings.