Twenty-slide deck. Twenty sheets of A4 is a waste of paper for a five-minute reference. Two-up (two slides per sheet) cuts it in half. Four-up cuts it to five sheets.
Most printers handle this in the dialog. The PDF doesn't need changing.
Use the print dialog's N-up option
Adobe Reader: Print → Page Sizing & Handling → Multiple. Choose 2, 4, 6, or 9 pages per sheet. Preview: Print → Layout → Pages per Sheet.
No PDF editing needed. The printer does the layout work.
Pick the right N
2-up: pages stay readable, save half the paper. 4-up: smaller but legible for slides. 6-up or 9-up: thumbnail-style, only useful for visual reference.
For text-heavy PDFs, 2-up is the most you can comfortably read on A4. For slide decks, 4-up usually works.
Test before printing the lot
Print one sheet at the chosen N. Check readability. If text is too small, drop to a lower N. If you've got headroom, try a higher N for more savings.
FAQ
Will the printer adjust margins automatically?
Yes. N-up mode tiles pages within the sheet's printable area, adding gutters between tiles.
Can I do this with a slide deck?
Yes — and slide decks are the most common case. 4-up handouts are a presentation classic.
What about double-sided N-up?
Combine N-up with duplex printing for maximum paper savings. 4-up duplex = 8 PDF pages per physical sheet.
Does N-up work for booklets?
Booklet mode includes 2-up by default (two pages per side of each folded sheet). Use booklet mode rather than N-up for proper booklets.
N-up printing saves paper and creates instant handouts. Set it in the print dialog; the PDF stays untouched. For PDF prep, use Flint's editor.