How to Reduce PDF File Size for Email Attachments
Compress PDF Shrink a PDF to under 100 KB, 200 KB, 500 KB, or 1 MB — or just optimize it.You attach a scanned contract, hit send, and the message bounces back: attachment too large. It is one of the most reliably annoying moments in office work, and it happens because a document that looks like a few pages of text is, technically, a stack of photographs.
The actual limits
Knowing what you are aiming for helps, because the published limit is often not the effective one:
| Provider | Limit |
|---|---|
| Gmail | 25 MB |
| Outlook / Microsoft 365 | 20 MB (often lowered by company policy) |
| Yahoo Mail | 25 MB |
| Many corporate mail servers | 10 MB, sometimes 5 MB |
Two catches. First, the recipient’s limit matters as much as yours — you can send 20 MB and still have it rejected on arrival. Second, attachments are encoded for transport, which inflates them by roughly a third. A “25 MB limit” realistically means keeping the file under about 18 MB.
A sensible target: under 1 MB. At that size no mail server anywhere will object, and the message stays pleasant to receive.
Why scanned PDFs are so large
A page of text exported from Word is a few kilobytes — it is instructions for drawing letters. A scanned page is a photograph, often at 300 or 600 DPI. At 600 DPI an A4 page is roughly 35 million pixels. Ten pages of that, and you have a file that no amount of zipping will meaningfully shrink, because the image data is already compressed.
Office scanners default to settings far higher than anyone needs for a readable document, which is why a ten-page scan routinely arrives at 40 MB.
The fix
- Open Compress PDF.
- Drop your file in — the current size is shown immediately.
- Choose a target. Under 1 MB is the right choice for email.
- Click compress, check the before/after size, and download.
Everything happens in your browser: the document is never uploaded. That matters for the kind of files people send as attachments — contracts, invoices, medical letters, application papers.
For a typical multi-megabyte scan, getting under 1 MB usually costs almost nothing visually, because the source was wildly over-sampled to begin with.
When compression isn’t the right answer
Sometimes the file is large for a reason, and squeezing it is the wrong move:
- The document must stay high-resolution — print artwork, architectural plans, anything destined for a printer. Compressing destroys exactly what makes it useful. Send a download link instead.
- You need the text to stay selectable. Strong compression converts pages to images, so the text is no longer searchable or copyable. If the recipient needs to search the document, compress less aggressively (choose “best quality” rather than a hard target) or send the original.
- It is genuinely a huge document. A 400-page manual is legitimately large. Use a cloud link.
Alternatives worth knowing
Send fewer pages. Often the recipient needs three pages, not the whole bundle. Split PDF extracts just what is relevant — the fastest way to shrink an attachment is to send less of it.
Split into parts. If everything genuinely has to go and each file must stay small, split the document into two or three files and send them as separate messages.
Use a link. For anything above a few megabytes, a shared link is more considerate than an attachment: it does not clog the recipient’s mailbox and it keeps working after the message is archived.
Don’t bother zipping. A ZIP of a PDF typically saves a few percent, because the PDF’s contents are already compressed. It just adds a step for the recipient.
How much smaller can you expect?
Rough expectations, so you know whether a result is normal or whether something is wrong:
- Phone or flatbed scans — typically shrink by 90–95%. A 20 MB scan landing at 800 KB is completely normal, because the source was massively over-sampled.
- Photo-heavy documents (brochures, reports with images) — large gains, since the embedded photos dominate the file size.
- Text-only PDFs exported from Word — barely shrink at all, and that is expected. There is no photographic data to compress; the file is already small and efficient. If a 300 KB text PDF refuses to get smaller, it is not a fault, it is simply already optimal.
If a file will not compress and it is already under a megabyte, stop trying — you are optimising something that is not the problem.
Scanning better next time
If you scan documents regularly, changing the default settings once saves you this problem permanently:
- 200–300 DPI is plenty for a readable text document. 600 DPI is for archival photo reproduction.
- Grayscale or black-and-white for text documents. Colour roughly triples the size and adds nothing to a signed contract.
- Use your phone’s document mode rather than a plain photo — it crops, straightens, and cleans the page, which compresses far better than a snapshot of a desk.
Other size targets
If you are working to a specific number rather than just “small enough for email”:
- Compress PDF to 100 KB — government and exam portals
- Compress PDF to 200 KB — job applications, university admissions
- Compress PDF to 500 KB — tenders, insurance, court e-filing
- Compress PDF to 1 MB — email and general uploads
Frequently asked
Will the quality be visibly worse? For a typical scan compressed to 1 MB, usually not — there is enough headroom that the gentlest setting is sufficient. Aggressive targets like 100 KB are a different matter.
Does it change my original file? No. A new compressed copy is created; the original stays untouched on your device.
Is it free? Yes — no signup, no watermark, no file count limit.