This is the 13th most frequent Croatian word.
do
"Do" in Croatian means "to" or "until."
In this sentence, 'do' is used to indicate a deadline, equivalent to 'by' in English.
Do sutra moramo završiti projekt.
By tomorrow, we must finish the project.
Here, 'do' specifies a point of reach, meaning 'up to' in English.
Do vrata je stigao trčeći.
He reached up to the door running.
In this context, 'do' denotes a time limit or extent, similar to 'until' in English.