A PDF that will not attach or upload is a common phone problem. Forms ask for a file under 200 KB or 2 MB, email apps refuse large attachments, and the PDF you scanned on the bus is 14 MB. You do not need a computer or a new app to fix it.
Why a scanned PDF is so big
A PDF made from typed text is small, often a few tens of kilobytes. A PDF made by photographing or scanning pages is different: each page is a full-size photo, and a ten-page scan is ten large photos. Phone cameras take pictures with many millions of pixels, far more than any form needs. Shrinking those pictures is where almost all the savings come from.
A quick test: open the PDF and try to select a word. If you can, it is mostly text. If you cannot, it is mostly pictures, and compression will help a lot.
Reduce a PDF in your phone browser
The steps are the same on iPhone (Safari) and Android (Chrome, Firefox or any other browser).
- Open Compress PDF in your browser.
- Tap the drop area and choose your PDF from Files, Downloads, iCloud Drive or Google Drive.
- Choose how to shrink it. Pick a quality level for a light squeeze, or tick the target size option and type the number of KB your form allows.
- Tap Compress and wait. Each page is re-drawn on your phone, so long documents take longer.
- Check the before and after sizes shown, then save the new copy. Your original file is not changed.
On an iPhone the saved file goes to Downloads in the Files app unless you choose another place. On Android it goes to your Downloads folder. The PDF is processed on your device and is not uploaded to a server, which matters when it is an ID, a contract or a medical record.
Aim for the number the form gives you
If a form says the file must be under a certain size, type that limit into the target box, then leave a small margin. Some systems count 1 MB as 1,000,000 bytes and others as 1,048,576, so a file that is just under on your phone can still be rejected. These pages are already set up for common limits:
- Compress PDF to 200 KB for job and admission portals.
- Compress PDF to 1 MB for most email and claim uploads.
- Compress PDF to 2 MB, pre-set to 1,800 KB to leave a margin.
If it is still too big
Page count is the main lever, because the size budget is shared across all pages. A few things help before you compress again:
- Send only the pages needed. Use Split PDF to keep the pages the form asks for.
- Remove blank pages. Back-sides of scans add weight for nothing. Remove blank pages finds them.
- Try grayscale. If colour does not matter, converting to grayscale often shrinks a scan.
- Rescan at lower quality. If you can, scan again in black and white or at a lower resolution, rather than shooting a full-resolution photo of each page.
What compressing costs you
To make pages small, the tool saves each one as a picture at lower quality. That means the text in the new file can no longer be selected, searched or copied. Keep your original and send the compressed copy only where a size limit forces you to. Fine print and thin lines are the first things to blur, so zoom in and check the result before you submit it.
Privacy on a phone
Phones hold the documents people care about most: passports, payslips, medical letters and signed forms. Many online compressors upload the file to a server, keep it for some time, and ask you to trust their deletion policy. DocPro's compressor does the work inside your browser tab, so the file never leaves the phone.
Keeping the result usable
- Save under a new name, such as the original name plus 200kb, so you do not send the wrong version later.
- Open the compressed copy and scroll through every page before you attach it.
- Keep the screen on while a large scan is processing. A phone that goes to sleep may pause the work.
For a longer explanation of what makes PDFs big and what each option costs, see How to compress a PDF for email and upload limits.
Frequently asked questions
Is there a built-in way to compress a PDF on iPhone?
Not a simple one. The Files app can zip a file, which helps with email size a little, but the recipient has to unzip it, and many upload forms reject zip files. A browser tool that makes the PDF itself smaller is usually the better route.
Can I compress a PDF on Android without an app?
Yes. Open a browser tool such as Compress PDF in Chrome or Firefox, pick the file from your downloads or Drive, and save the result. Nothing needs to be installed.
Will the PDF look worse after compressing?
Slightly, mostly in photos and scanned pages. A light compression is hard to see. A very small target, such as 100 KB for many pages, makes pages soft, so check the result before you send it.