WhatsApp caps PDF attachments at 100MB. Here's the fastest free way to shrink a large scanned PDF for WhatsApp — works on any phone or laptop, no app.
WhatsApp's hard cap on document attachments is 100MB across iOS, Android and WhatsApp Web. If your PDF is larger, you'll see 'File too large' the moment you try to attach it — there's no warning before that, and no Premium tier to pay for a higher cap.
The 100MB limit is generous compared to Gmail (25MB) or Outlook (20MB), but scanned documents can blow past it surprisingly fast. A 50-page colour scan at 300 DPI easily hits 200–400MB.
Almost every oversized scanned PDF is bloated by one of two things: scans saved at unnecessarily high DPI (600 DPI when 150 is fine for screen reading), or full-colour scans of black-and-white documents. The second one is the silent killer — a colour scan of a printed page is roughly 8x larger than the equivalent greyscale scan.
Open Compress PDF in any browser — works in mobile Safari, Chrome on Android, and on the laptop next to you. Drop the PDF onto the dropzone, pick the Strong compression preset, and click Compress.
For typical scanned documents, expect a 50MB original to drop to 3–8MB. That's well under the 100MB WhatsApp cap with margin to spare for very large originals.
If you're on iPhone and scanned with the Notes app, the resulting PDF is usually already compressed reasonably well — you may only need the Recommended preset, not Strong.
If you're on Android and used Google Drive's scanner, the output is often higher-DPI than necessary. Strong compression typically halves it without visible quality loss.
WhatsApp's hard limit is 100MB. Use Compress PDF Strong preset — most scanned documents drop to under 10MB.
No — unlike images, WhatsApp does not re-compress document attachments. The recipient gets the exact file you sent.
Yes. Open Compress PDF in mobile Safari, pick the file from Files or iCloud, compress, save back to Files, then attach in WhatsApp.