How to Compress a PDF on iPhone or iPad (Files, Shortcuts, and the Print-to-PDF Trick)

The situation

You are on your iPhone or iPad, you have a PDF to send, and the app you are using says it is too big. A scanned form, a batch of receipts, or a document someone shared with you has ballooned past an email or upload limit, and you do not have a computer nearby.

Here is the honest part: unlike a Mac, iOS has no built-in slider that simply shrinks a PDF. There is no single "reduce file size" button in the Files app. So the practical approaches are a handful of workarounds, and it helps to know which one fits your situation before you start tapping around.

Why iPhone PDFs get big

Most large PDFs on a phone come from scanning. When you use the built-in scanner in Notes or Files, or a third-party scanner app, each page is captured as a high-resolution photo and wrapped in a PDF. A few color pages can easily reach tens of megabytes.

PDFs you receive can also be heavy for the same reason: embedded photos, screenshots, or image-only scans. If a file is large, it is almost always picture data rather than text, which is why simply re-saving or re-encoding the images shrinks it so much.

Method 1: The print-to-PDF re-save trick

This is the classic no-app route and often helps with scans.

1. Open the PDF, then tap the Share icon.
2. Choose Print from the share sheet.
3. On the print preview screen, pinch outward on the page thumbnail as if zooming in. This reopens the document as a fresh PDF.
4. Tap Share again from that preview and save it back to Files.

The re-saved copy is sometimes smaller because iOS rebuilds the document. Results vary a lot by file, so check the new size in Files. If it barely changed, move on to a tool that targets size directly.

Method 2: A Shortcuts automation

The Shortcuts app can rebuild a PDF, which can trim overhead.

1. Open Shortcuts and create a new shortcut.
2. Add an action that accepts a PDF or an image as input.
3. Add a "Make PDF" action, and if you first convert pages to images you can lower their quality before rebuilding.
4. Add a "Save File" action and run the shortcut, then share it to the share sheet so you can reuse it.

Shortcuts is flexible but fiddly, and it still does not let you name an exact target size. It is best if you compress files often and want a repeatable tap.

Method 3: Aim for an exact size in the browser

When a portal or email rule gives you a hard limit, the workarounds above are guesswork. A target-size tool solves that directly, and it works in mobile Safari with no app to install.

1. In Safari, open your PDF or have it ready in Files.
2. Go to PDF300.
3. Upload or select the PDF, then enter the target size you need, such as 20 MB.
4. In PDF300, download the compressed file; it saves straight to your device.

Because PDF300 offers an in-browser mode that re-encodes the file locally, a private document can be compressed without ever leaving your phone.

Checklist

• Check the current size first by long-pressing the file in the Files app and viewing its info.
• Try the print-to-PDF re-save trick for scans; it costs nothing and takes seconds.
• Keep the original until you confirm the smaller copy still reads clearly.
• If you need an exact limit, use a target-size tool in Safari instead of guessing.
• For anything sensitive, choose a route that processes the file on the device.

FAQ

Is there a built-in way to shrink a PDF on iPhone?

Not directly. iOS has no dedicated PDF compression slider, so you rely on workarounds like the print-to-PDF re-save, a Shortcuts automation, or a web tool. The Files app can view and organize PDFs but will not reduce their size on its own.

Why is my scanned PDF from my phone so large?

Scanner apps capture each page as a high-resolution image, so a few color pages can reach tens of megabytes. The text you see is actually a picture, which is why the file is heavy. Re-encoding those images at a lower resolution is what brings the size down.

Can I compress a PDF on my iPhone without installing an app?

Yes. The print-to-PDF trick and Shortcuts are built in, and a browser tool like PDF300 runs in Safari with nothing to install. Its in-browser mode re-encodes the file locally, so the document stays on your phone.