To reduce PDF size for email, compress the images inside the file rather than the text — that is where nearly all the weight sits. Drop the file into Compress PDF and it re-encodes the embedded images at a screen-friendly resolution on your own device, typically taking a 20 MB scan down to a few megabytes. Nothing is uploaded, so the document stays private even while you are getting it under an attachment limit.
What the attachment limits actually are
Gmail caps attachments at 25 MB per message, and Outlook.com applies the same 25 MB ceiling for standard attachments. Microsoft 365 and Exchange mailboxes often default to a stricter 20 MB, and an administrator can lower that further, so a file that leaves your outbox fine at work may bounce for a recipient elsewhere. There is also a hidden catch: email encodes attachments in base64 before sending, which inflates them by roughly 33%. A 24 MB PDF can therefore arrive on the wire at over 32 MB and be rejected by a limit you thought you were under. Treat about 18-20 MB as the practical safe ceiling for a 25 MB service.
Why your PDF is so large in the first place
Text and vector graphics are extremely compact. A 40-page text-only report is often under 1 MB. The files that break email limits are almost always image-heavy: phone photos of documents, flatbed scans saved at 600 DPI, exported slide decks, or screenshots pasted into Word and then printed to PDF. A single full-resolution phone photo can be 4-6 MB, so a ten-page scanned contract is comfortably past 25 MB without containing a single kilobyte of real text.
That is why "zip the PDF" rarely helps. PDFs already store their images in compressed form, so a ZIP archive typically shaves off only a few percent. The only way to make a meaningful dent is to re-encode the images themselves.
The fastest route: compress on your own device
- Open Compress PDF and drop the file in. It is read into your browser's memory, not sent anywhere.
- Each page is re-rendered at a resolution suited to screen reading and the images are recompressed.
- Download the smaller PDF and attach it. Check the new file size in your file manager before you send.
This matters more than it sounds when the PDF is an invoice, a signed contract, a payslip, or a medical letter. Most online compressors upload your document to a server to do the work. A browser-based tool does the same job locally, so the file never leaves your machine — it will even run with your Wi-Fi switched off, which is the simplest proof there is no upload happening. It is free, unlimited, and needs no account.
Be realistic about what compression can and cannot do
Compression trades resolution for size. A scan re-encoded for screen viewing will look identical at normal zoom but will be softer if you zoom right in or reprint it at full page size, and fine print in a low-quality original can tip from marginal to unreadable. Keep the original file if you may need to print or archive it later, and always open the compressed version before you send it.
If your PDF is mostly text and it is still large, compression will do very little, because there was never much image data to squeeze. In that case the file is usually large for a different reason: embedded fonts, an enormous page count, or attachments buried inside it.
What to do when compression is not enough
- Send only the pages that matter. Split PDF extracts a page range into its own file, and Delete Pages strips out the ones the recipient does not need.
- Building the PDF from photos yourself? Skip the bloat entirely and assemble a right-sized document from the start with Images to PDF.
- Sending several documents? Combine them with Merge PDF first, then compress once — one pass over the merged file beats compressing each piece.
- If the recipient only needs the words, PDF to Text or PDF to Word will produce a file a fraction of the size.
As a last resort, share a cloud link instead of an attachment. That defeats the privacy benefit of keeping the file on your own machine, so reach for it only when the document genuinely cannot be made smaller.