PDF Combiner
The attachment bar spins for a moment, and then the message bounces: the file is too large to send. Usually it’s a scan — six pages of a signed contract that somehow weigh 38 MB.
Fixing it takes about a minute, as long as you go after the right part of the file.
Why a scanned PDF is so heavy
A PDF is a container, and what’s inside decides the weight.
- A scanned or photographed PDF is a stack of images. Each page is a full-resolution photo. Ten pages of text that would be 200 KB as actual text can easily be 40 MB as pictures of text.
- A PDF exported from a document is mostly text. Fonts and characters — a few hundred kilobytes, even for a long file.
This is worth thirty seconds of your attention, because it decides whether compressing is worth trying at all. If the file came out of a scanner, a copy machine or your camera, there’s a lot to squeeze and compression can cut it dramatically. If it was exported from Pages or Word, there’s almost nothing heavy inside and no compressor will do much — skip to sending it without compressing.
Compress a PDF on iPhone, iPad or Mac
Here’s the flow in PDF Combiner. It’s the same on all three, and everything happens on the device.
- 1
Open Compress PDF and add the document
Pick the file from Files, iCloud Drive or your device. On a Mac the tool is called Compress on the main screen and opens a window titled PDF Compression. Your original isn’t touched — you’ll get a separate, smaller copy.
- 2
Choose a Quality level
Three settings: High, Medium, Low. They describe the quality you keep, not the compression you apply — High preserves the most detail and shrinks the file least; Low is the most aggressive.
Start at Medium for a scan of an ordinary printed page. Go to High when the page carries fine print, a stamp, a handwritten signature or a passport photo — anything a person will have to read closely on the other end.
- 3
Generate and save it under a new name
contract-small.pdfbeats a file you can no longer tell apart from the original. - 4
Check the result before you send it
Open the smaller copy and zoom in on the smallest text on the busiest page. If that’s still legible, the whole document is fine. Still too big? Go back and step down one Quality level rather than jumping straight to Low.
Two things this handles that a one-off export doesn’t. You can run the same step across a batch instead of repeating it document by document. And if you’re merging several files — the classic way a document ends up oversized — you can merge and then compress the result in one sitting.
It also never leaves the device. No upload, no account, no connection required; it works in airplane mode. Most web-based compressors work the other way round: your file is uploaded, processed on someone else’s machine, and stored at least long enough to hand back a result. For a holiday itinerary, fine. For a lease, a medical result or a scan of an ID, that’s a decision worth making deliberately.
How small does it actually need to be
Most mail services stop somewhere around 20–25 MB per message, and a few are stricter. Aim comfortably under the limit rather than exactly at it — the message carries the attachment plus everything else, and a file that lands right on the number is the one that bounces.
What the built-in tools do — and don’t
Your Mac and your iPhone can both shrink a PDF on their own. It’s worth knowing exactly how far that goes.
On a Mac, open the PDF in Preview, choose File → Export, and pick Reduce File Size from the Quartz Filter menu. The same dialog has checkboxes for Optimize Images for Screen and Save Images as JPEG. It genuinely shrinks scans, but the filter is a single fixed pass with no quality dial — small text can come out soft and grey, and your only recourse is to try again. Export to a new file so the original survives the experiment.
On iPhone and iPad, the Preview app arrived in iOS 26. Tap the ⌄ next to the filename, then Export — and read the sheet carefully, because it’s built for images first:
- The format defaults to HEIC. Leave it there and you get a picture instead of a document — and for a scan it can come out larger than the PDF you started with: on a 1.4 MB scan, the sheet’s own Estimated file size for HEIC read 2.2 MB. Switch the format to PDF.
- Once PDF is selected, the Size slider disappears. What you get instead is Save Images as JPEG, Optimize Images for Screen and a Resolution field. Those are the levers that actually reduce a scan.
- There’s no target size and no preview of the result, so it’s a matter of exporting and checking.
What doesn’t work is the one everybody recommends. Long-press a file in Files and you’ll see Compress. That creates a .zip, and on a PDF it barely helps: the images inside are already compressed, and compressing compressed data gains close to nothing. You get a file that’s effectively the same size and that the recipient has to unpack first. Skip it.
When you don’t need to compress at all
Not every oversized PDF is a compression problem.
- Send only the pages that matter. If the recipient needs pages 4–7 of a 60-page report, Split PDF and Extract Pages produce a smaller and more useful file than any amount of compression. This is the most underrated fix on the list — how to split a PDF covers it.
- Shrink the photos before you build the PDF. If you’re about to combine a pile of camera shots into one document, resizing the images first does most of the work up front. (Compress & Resize Photos works on images; Compress PDF works on finished documents. Different jobs.)
- Scan instead of photographing. Scan Documents detects the page edges and crops to them, so you’re not carrying the desk, your hand and the tablecloth around inside the file at full resolution.
- Send a link instead of a file. From the Mail app with an iCloud account, an oversized attachment triggers an offer to send it through Mail Drop: messages up to 5 GB, and the recipient has 30 days to download. Or put the file in iCloud Drive and share a link to it from Files. Neither degrades the document at all — which makes them the right answer when the scan has to stay legible.
More walkthroughs like this one are in the PDF Combiner guides.