The German triumphed on home turf after strong winds and heavy rain first led to a postponement, before organisers decided on a one-run format.
Freitag was last on the start list but delivered a mighty leap to take the gold medal, and score 128.4 points.
Geiger rounds out World Cup season with flying finale
The 26-year-old is in excellent form at present and helped Germany to a third-place finish in the team event on Friday, Freitag also delivering the best jump of that competition at 143.5m.
The win is Freitag's seventh World Cup triumph of his career and extends his lead in the overall rankings on 370 points, 51 clear of his nearest rival and fellow countryman Andreas Wellinger.
Wellinger finished in second place having jumped 139.5 metres for 126 points. He now has 319 points and is second overall.
Norway's Daniel Andre Tande finished third, a position he also occupies in the overall standings, with Junshiro Kobayashi of Japan fourth on the day.
Kriznar claims ski jumping crystal globe after sensational season finale
'Absolutely superb' - Geiger jumps to victory in Planica