How to Compress a PDF on iPhone
· Updated · 5 min read · By Furkan Kaya
Quick answer
The built-in way to compress a PDF on iPhone is a Shortcuts shortcut: add the Optimize File Size of PDF action plus Save File, turn on Show in Share Sheet, then share the PDF from Files and run it. If the PDF is made from photos or scans, shrink the images first with a free image compressor, then rebuild the PDF.
"The attachment is too large." It's one of the most annoying errors on a phone, and it usually shows up right when you're trying to send a scanned contract, a portfolio, or a form. The fix is to compress the PDF so it fits the size limit — and you can do it on your iPhone in a few minutes.
Why PDFs get so big (and how compression helps)
A PDF's size is almost always driven by the images inside it — especially scanned pages and high-resolution photos. A multi-page scan can quickly pass the roughly 20–25 MB limit many email services allow. Compression re-encodes those images at a sensible resolution, which can shrink the file considerably while keeping the pages readable. Text-only PDFs are usually small already and won't shrink much.
Built-in method: compress a PDF with Shortcuts
- Open Shortcuts, tap + and add the action Optimize File Size of PDF.
- Add Save File after it so you can choose where the smaller copy goes.
- In the shortcut's settings (ⓘ), turn on Show in Share Sheet and allow PDFs.
- Open the PDF in Files, tap Share and run the shortcut. Long-press the new file and tap Get Info to compare sizes.
This runs on your iPhone, so the document never leaves the device. Results depend on the PDF: scanned pages shrink the most.
PDF made from photos? Compress the images first
If you're about to turn photos or scans into a PDF, it's easier to shrink the pictures before building the PDF. Run them through the free image compressor in Safari (nothing is uploaded), then combine them with the JPG to PDF tool. Too many pages? Send only the ones you need with the Split PDF tool.
Using the ConvertEase app
The ConvertEase iPhone app can also compress PDFs and Office documents. To be clear about how: document compression runs on ConvertEase's server, so the PDF is uploaded for processing (image, video and audio compression run on the iPhone). The app is free to download; saving results requires a Premium subscription. For very sensitive documents, prefer the Shortcuts method.
Which compression level should I choose?
| Goal | Recommended level | Result |
|---|---|---|
| Email a scanned document | Medium / "Email" | Big size cut, fully readable text |
| Upload to a portal with a strict cap | High | Smallest file, slightly softer images |
| Archive but keep it crisp | Low | Modest size cut, near-original quality |
Tip: compress before you sign or send
If you scanned a multi-page document with the Camera or Notes app, it's worth compressing it before attaching. You'll avoid the "file too large" bounce-back entirely, and the recipient downloads it faster too.
Shrink scans before they become a PDF
Free · runs in Safari · images are not uploaded
Open the image compressorFrequently asked questions
Build a Shortcuts shortcut with the Optimize File Size of PDF action and run it from the PDF's share sheet; it works on the iPhone. If you are making the PDF from photos or scans, compress the images first and then build the PDF. The ConvertEase app can also compress PDFs, but it does so on ConvertEase's server, so the file is uploaded.
Most email providers cap attachments at around 20–25 MB. PDFs that contain scanned pages or high-resolution images can easily exceed that. Compressing the PDF reduces the size of those embedded images so the file fits within the limit.
Compression mainly shrinks the images inside the PDF. A balanced setting keeps text crisp and pages readable while cutting the size noticeably. Text-only PDFs are usually small already and shrink very little.
The Shortcuts method runs on your iPhone, so the document stays on the device. Any service that compresses PDFs on a server — including the ConvertEase app, which processes PDF and Office compression on its server — requires uploading the file, so use the built-in method for highly sensitive documents.
The app is free to download; saving compressed files requires a ConvertEase Premium subscription. PDF compression in the app runs on ConvertEase's server, while image, video and audio compression run on the iPhone.