Less paper for the same document
Slides, lecture notes, long manuals and reports often print one page per sheet even though each page has little on it. With two pages per sheet, a 60-page document fits on 30 sheets; with four, on 15; and printed on both sides, the stack gets thinner still. It is the classic way to print a slide deck as study notes or a long article to read with a pen.
Some printers offer a similar setting in their own dialog, but it changes from one driver to another and not every app has it. Doing it in the PDF gives you a file that prints the same on any printer, that you can send to a copy shop, and that you can check page by page before printing.
How the pages are laid out
You can choose 2, 4, 6, 8, 9 or 16 pages per sheet, on A4 or Letter paper. The pages are placed in reading order: from left to right and from top to bottom, like the lines of a book. Each page is scaled to fit its cell without changing its proportions.
An optional gap separates the pages, and an optional thin border draws a frame around each one, which helps the eye when the pages have white backgrounds. As a rough guide, 2 or 4 per sheet stays comfortable to read, 6 to 9 suits slides with large text, and 16 is more of an overview or a quick proof.
Sharp text, but some things are lost
The pages are not turned into images: text stays as real text, so it prints sharp even when it is small, and you can still select and search it in the new PDF. What does not survive is interactivity. Links and form fields from the original are lost, so if you need to fill in a form, do that first and arrange the pages afterwards.
Keep in mind that more pages per sheet means smaller text. Before printing the whole document, look at the result on screen, or print one sheet, to make sure the size is still readable.
Private, free and on any device
The new PDF is put together in your browser, so your document is never uploaded and nothing is stored. It is free, with no account, no watermark and no limit on how many files you prepare.
If you want to fold the printed sheets into a small booklet, use “PDF to booklet”, which reorders the pages for that. To change the paper size without combining pages, use “Resize PDF”. Password-protected files must be opened with “Unlock PDF” first.