A PDF is a fixed document. A PowerPoint file is an editable slide deck. Converting from PDF back to PPT is useful, but it is not magic: the converter has to infer text boxes, images, and layout from a flattened page.
The best results come from PDFs that were originally exported from slides. Scanned PDFs, photographed pages, and design-heavy brochures may convert as images or need cleanup after conversion.
Use PDF to PPT when you need to update an old presentation, reuse slides, or recover a deck when the original file is missing.