Rebuild mode turns each page back into separate text boxes, pictures and shapes you can change. Picture mode pastes each page as one image: perfect-looking, but nothing to edit. Click the parts of a slide to see what each became.
We converted one source document into every major output format and measured the file that came out. The source was a 37.4 KB DOCX with headings, bold and italic text, a table, numbered and bulleted lists, and one embedded image.
Sizes are from one representative document converted with Pandoc and LibreOffice. Your own files will differ, especially with more images, but the relative ordering holds.
A PDF has no paragraphs. It stores “draw these glyphs at x, y in this font”, often one word or one line at a time, and a scanned page stores only a picture. Drop any PDF to see which kind you have and what its page instructions look like.
If your PDF is a report rather than a deck, its pages are tall and a projector is wide. There are three ways to reconcile them, and each gives up something different.
A PDF stores drawings, not PowerPoint objects. Some parts rebuild cleanly; others can only return as pictures.
Most PDFs of slides started life as a deck. Saving to PDF flattened the parts that only exist while presenting. They can't be recovered from the PDF: ask the author for the original file if you need them.
PDF was saved as “Notes pages”Each page shows the slide on top and speaker notes belowConverting the whole deck isn't always the fastest way to what you're after.