What are the low ink problems?

[Holy Cross]

I send a document to print in black. Instead, it prints in red. Does Word
automatically select if the black cartridge is low in ink?

 

[Suzanne S. Barnhill]

This would more likely be a function of your printer. Many inkjet printers
use composite black for envelopes and other small documents, which you may
not notice until the color cartridge is low on one or more colors of ink.

 

[Jezebel]

Word knows nothing at all about the physical printer. Word simply sends the
file to the printer driver. What happens after that is between the printer
driver and the physical device.