Synonym of undocumented immigrant
"She works long hours at a local diner but remains undocumented, afraid to speak up about her wages for fear of deportation."
lacking necessary documents (as for e.g. permission to live or work in a country)
"undocumented aliens"
"undocumented tax deductions"
Lacking instructions or reference material.
"The new software update was undocumented, leaving us to figure out how to use the new features without any manual or guides."