PPTX 转 PPT
把现代版 PowerPoint 演示文稿存成经典的 PPT 格式，供 PPTX 出现之前的旧版 PowerPoint 使用。
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To
PPTX
The modern PowerPoint presentation format, used by PowerPoint, Keynote, and Google Slides.
PPT
The legacy PowerPoint format from before 2007, still found in older slide decks.