How to Compress a PDF for Email — Gmail, Outlook and beyond

Why your PDF won't send

You hit send, the spinner crawls, and then comes the bounce: "Attachment too large." It's one of the most common email frustrations, and almost always caused by a single, predictable culprit — a PDF carrying high-resolution images, embedded fonts, or both.

The good news is that you almost never need to delete pages, scan again, or hunt for a different file format. A single compression pass typically shrinks a PDF by 40–70% with no visible loss of quality on screen — usually enough to slip safely under any email provider's cap.

This guide walks through exactly how to do that, when to choose which compression level, and the handful of cases where compression alone is not enough.

Email attachment size limits by provider

Different providers cap attachment sizes at different ceilings. Knowing your target before you compress saves time:

The practical safe target for general use is under 20 MB. That sails through every consumer provider and most corporate gateways. If you do not know what the recipient uses, aim for under 10 MB — that clears even strict corporate filters.

How to compress your PDF — step by step

Compressing a PDF using PdfDocShift takes three steps and runs entirely in your browser. Nothing to install:

Which compression level should you choose?

The right level depends on what is inside your PDF and what the recipient will do with it.

Low — for the smallest possible file

Aggressively downsamples images to 72 DPI and strips most metadata. Best for internal archives, draft sharing, and uploads to portals with very strict size caps. Quality loss will be visible on image-heavy documents — fine print on diagrams may become harder to read.

Medium — the recommended default

Resamples images to 150 DPI — sharp enough for on-screen reading and standard printing — while typically reducing file size by 40–70%. This is the right setting for emailing reports, sending invoices, sharing portfolios, and almost every everyday case. If you only choose one setting, choose this one.

High — when fidelity matters

Applies minimal compression, preserving images close to their original resolution. Reduction is smaller (typically 10–30%), but the result is visually almost identical to the source. Use this for documents that will be printed professionally or that need to pass careful visual inspection — design proofs, photo books, official contracts with embedded scans.

What if your PDF is still too large?

Sometimes Medium compression is not enough — you started from a 200 MB PDF and Medium only got it down to 60 MB. You have three good options:

Option 1 — Try Low compression first

If the document is mostly for on-screen reading, Low will often shave another 30–50% off the file size with quality loss most readers will not notice.

Option 2 — Split the PDF into smaller files

Use the Split PDF tool to break a long document into two or three smaller files, then send each as a separate email. This works well for reports with clear section breaks. Number the resulting files (report-part-1.pdf, report-part-2.pdf) so the recipient knows the order.

Option 3 — Send via a cloud link instead

If the file simply has to stay intact at full size, upload it to Google Drive, Dropbox, or WeTransfer and email the link. Most providers do this automatically now: Gmail uploads anything over 25 MB to Drive and inserts a link in the message body without asking. iCloud Mail offers Mail Drop. This avoids compression entirely and works for files up to several gigabytes.

Why email providers cap attachment size

Email attachment limits feel arbitrary, but the reasons are practical:

• SMTP overhead. Email attachments are base64-encoded for transit, which inflates file size by roughly 33%. A 20 MB file becomes ~27 MB on the wire. Providers cap inbound size to keep their servers from getting overwhelmed.
• Storage cost. A copy of every attachment sits in the sender's Sent folder, the recipient's Inbox, and often a corporate archive. Large files multiply that cost across millions of users.
• Delivery reliability. Larger messages are more likely to fail mid-transit, be flagged as spam, or trigger anti-virus deep-scan delays. Caps keep delivery predictable.
• Recipient experience. Downloading a 50 MB attachment on a mobile connection is painful. Keeping attachments small respects the recipient's bandwidth.

This is why every modern email provider that allows larger files routes them through cloud storage with a link. The link approach lets the file live in one place, expires gracefully, and does not bloat anyone's inbox.

Tips to avoid oversized PDFs in the future

A bit of upstream care saves a lot of compression effort later:

• Export at the right resolution. When generating a PDF from Word, Pages, InDesign or Google Docs, choose "Standard" or "Smallest size" instead of "Print quality" unless the file is genuinely going to a print shop.
• Avoid pasting screenshots when text would do. A screenshot of a paragraph easily weighs ten times more than the same paragraph typed out.
• Scan at 200 DPI, not 600. For text scans, 200 DPI is sharp and searchable. 600 DPI is print-shop territory and multiplies file size accordingly.
• Crop generously. Unused margins increase image area, which increases file size. The Crop PDF tool can trim them after the fact.
• Run OCR after scanning. The OCR PDF tool adds a text layer to scanned documents — making them searchable without adding meaningful size.

Frequently asked questions