Complex sentence: Although documentary evidence is limited, we are sure that between 1669 and 1672 Reyning fought as a privateer captain with French or English letters of marque; his partner was one Jelle Lecat (probably born in Frisia as Jelle de Kat).
Split into simpler sentences: Although documentary evidence is limited, Reyning is believed to have fought as a privateer captain with French or English letters of marque between 1669 and 1672. His partner was one Jelle Lecat (probably born in Frisia as Jelle de Kat).