Merge PDFs with different page sizes, and decide whether to make them match

What happens to page sizes when you merge?

Nothing, and that is on purpose. The merge copies each page with its own fonts, pictures and size; nothing is redrawn. The options panel says so: Page size: keep each, and the result says Page sizes kept as they were; nothing re-rendered.

We merged 3 typical parts and measured the pages:

The first 2 are close, and most viewers show them side by side without anyone noticing. The third is the one that makes the file look broken: zoomed to fit, the receipt fills the screen while the A4 pages look like stamps, and printed it is shrunk onto 1 sheet.

Keep the sizes or make them match?

How do I make every page A4, step by step?

Resize first, then merge, because resizing builds new pages and leaves bookmarks behind. Done in this order, the merge still adds 1 bookmark per file.

1. Open Resize PDF and drop all the parts at once, or their folder. They are resized 1 by 1, as a batch.
2. Paper: A4 (or Letter, Legal, A3, A5).
3. Margin: leave 0, or type a few mm if your printer cannot print to the edge.
4. Press Resize. The result says, for example, Put 3 pages on A4 paper, scaled to fit and centred, each the way up it was. Each file comes back with -a4 added to its name.
5. Download all (3) as zip (with your count), or in Chrome and Edge Save to a folder.
6. Open Merge PDF, drop the resized files, put them in order with Up and Down, and press Merge.

If you already merged, you can resize the merged file directly. In our test the merged file’s 3 bookmarks were gone after resizing, so do it this way only when you do not need them.

What Resize does to each page:

• Scales to fit, never crops or stretches. The page keeps its shape; a page of another shape gets white space at the sides or top and bottom. There is no crop-to-fill option. To trim margins, use Crop PDF first.
• Scales down and up. A Letter page comes out about 2.7 % smaller on A4; a small receipt page would be enlarged to fill the A4 page.
• Keeps landscape pages landscape, on landscape A4.
• Keeps text as text. Each page is placed as a vector copy, so text stays selectable and sharp.

Phone photos: fix them before they become pages

The giant page in the table came from a photo made into a PDF with Same as the picture. Phones tag their photos with 72 dpi, and a 4032 by 3024 pixel photo at 72 dpi is 56 by 42 inches, a page of about 1067 by 1422 mm.

The fix is at the source. In JPG to PDF, set Paper to A4 (it is the default) with Fit, and the photo becomes an ordinary A4 page; in our test the same photo came out at 210 by 297 mm. Then merge. The guide on picture page sizes goes deeper into paper, margins and orientation for photos.

The honest part: scaling changes the scale

• Everything on the page scales together. A Letter page put on A4 is about 2.7 % smaller, and a Legal page much more. For reading that does not matter. For a form that must print at 1 to 1, a plan with a printed scale, or a label sheet, it does: leave those at their own size. The guide on printing a PDF right covers printing mixed sizes without changing the file.
• Links, form fields and comments are not carried over by Resize PDF; the result says so when a file had them. Fill or flatten a form first.
• Bookmarks are not carried over by Resize PDF either, which is why the steps resize before merging.
• No crop to fill. Resize only fits. A page of a very different shape, such as a long receipt, gets wide white margins on A4.

Merge and Resize run in your browser, on your device; nothing is uploaded, and there is no limit on files or pages beyond your device’s memory.