How to compress a PDF on your phone
How do I make a PDF smaller on my phone?
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Short answer
Open a compression page in your phone's browser, choose the PDF from your files, pick a size such as 1 MB or 2 MB, and download the result — no app is needed. The work happens in the browser on your phone, so the file is not uploaded. If the PDF is in iCloud, Google Drive or OneDrive, make sure it has been downloaded to the phone first, or the browser may not be able to read it.
The steps
- Open Compress PDF in Safari, Chrome or any other browser on the phone. If a form has told you the limit, open the page for that size instead: under 1 MB, under 2 MB or under 500 KB.
- Tap the button to choose a file. The phone shows its own file picker: on an iPhone the Files app, on Android your downloads and storage.
- Choose the PDF and start the compression. A long scanned document can take a minute on a phone; keep the screen on.
- Download the result. It goes where the browser keeps downloads, usually the Downloads folder or the Files app.
"The file could not be read"
This is the commonest problem on phones, and it is rarely the PDF's fault. A file stored in iCloud Drive, Google Drive or OneDrive can appear in the file picker before it has been downloaded to the phone. The browser is handed a placeholder, and there is nothing in it to read.
Open the file once in the Files app or the Drive app so it downloads fully, or save a copy to the phone, then choose it again. A PDF that arrived as an email attachment is safest saved to the phone's files before you pick it.
Large files on small phones
Compressing runs on the phone's own processor and memory. A 20-page document is no trouble; a 300-page scan of 100 MB can be more than an older phone's browser will hold, and the page may reload or report that it ran out of memory.
- Close other tabs and apps, then try again.
- Split the document first and compress the parts — Split PDF also runs on the phone.
- Or do that one file on a computer, where the browser has more memory to work with.
How large a PDF can a browser handle has the details.
Sending the smaller file
After downloading, the share button on the result can hand the file straight to Mail, WhatsApp or another app on most phones, without looking for it in your downloads. Check the result before you send it: open it, zoom in on the smallest print, and make sure it is readable. If it has to fit a strict limit, how to compress a PDF to a specific size explains why aiming slightly under the limit is safer.
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Sources
Primary documentation for the claims above.