iPhone doesn't have a dedicated PDF compression tool built in, but there are two reliable approaches — one that uses only what's already on your phone, and one through a browser that gives you more control over the result.
The Built-In Method: Print to PDF
Open the PDF in the Files app and tap the Share button. In the share sheet, tap Print. On the print preview screen, use a pinch-to-zoom gesture — spread two fingers apart on the preview thumbnail. This opens the page as a full PDF preview in a new screen. Tap the Share button from this new screen and save to Files. iOS re-renders the PDF at a lower resolution during this process, reducing file size automatically.
This method is quick and requires no internet connection, which makes it useful when you're offline or dealing with a confidential document you'd prefer not to upload anywhere. The tradeoff is that you can't control the compression level — iOS applies a fixed setting that works well for text documents but can visibly degrade photo-heavy PDFs. Check the output before sending by zooming in on image areas to confirm quality is acceptable.
Browser-Based Compression: More Control
Open Safari and go to WukongPDF's PDF Compression tool. Tap the upload button and select the PDF from Files. After uploading, the tool compresses the file and provides a download link. Tap the link to download, then open the file from Safari's download manager to save it to Files.
The browser tool applies smarter compression than the print method — lossless for text and vector elements, optimized JPEG compression for images. For a PDF with mixed content (text and photos), this preserves text sharpness while still reducing the image data. The size reduction is typically similar to or better than the print method, with better quality for image-heavy documents.
Sharing the Compressed PDF Directly From iPhone
Once compressed, you don't need to save the file first to share it. From Safari's download manager, tap the file and choose Share to send it directly via Mail, Messages, WhatsApp, or any other app. For email attachments specifically, most email providers on iPhone accept up to 20-25MB — if your compressed file is under that, it can go straight into an email without saving to Files first.
When Neither Method Is Enough
For very large PDFs — 100MB or more — mobile browsers can struggle with the upload step. If the file is too large to upload via Safari, the most practical option is to move to a desktop or laptop for the compression step, or to split the PDF into smaller sections first using a PDF Editor tool, compress each section, and reassemble if needed.