How to Compress a PDF for Email (Without Ruining It)

By the ZypCRM editorial team · Updated 20 October 2026 · 5 min read

You attach a PDF, press send, and the email bounces – or your mail app refuses the file before you even try. Most of the time the fix is simple: make the PDF smaller. The trick is to make it smaller in the right way, so a CV stays searchable, a contract stays legible and a scanned form stays readable.

How big is too big?

Each email service sets its own limit on the total size of attachments in one message. Typical limits (check your provider, as they change):

Two details catch people out. First, attachments are encoded for transport, which makes them roughly a third larger, and some servers measure the encoded size. Second, the recipient’s server has its own limit, which may be lower than yours – company mail systems are often set to 10 MB. If the file is important, aim for under 10 MB, and ideally a few megabytes.

Why PDFs get large

A PDF is a container. Text and vector drawings take very little space; most of the size comes from images inside the PDF:

• Scanned documents are entirely images, one per page, often saved at 300–600 DPI in full colour.
• Phone “scans” and photos turned into PDFs carry camera-resolution images (12 megapixels or more per page).
• Design exports from tools like Word or Canva may embed full-size photos even if they appear small on the page.
• Embedded fonts add some size, but rarely more than a megabyte.

Knowing this tells you which approach will work.

Two kinds of compression

The Compress PDF tool offers two modes.

Lossless – keep text selectable

This mode rewrites the PDF’s internal structure more efficiently: it compresses streams, removes duplicated objects and packs data into object streams. Nothing visible changes, and text stays selectable and searchable.

Use it for:

• CVs and job applications (applicant tracking systems need real, selectable text)
• contracts and documents you might need to copy text from
• files that are already reasonably sized but bloated by inefficient software

The savings vary. A badly exported file may shrink by half; a PDF that is mostly photos may only shrink by a few per cent, because the photos themselves are not changed.

Strong – re-render pages as images

This mode draws each page and saves it again as a compressed JPEG image at the resolution you choose. It can shrink a large scan dramatically – often by 80–95%.

The trade-off is important: text becomes part of a picture. You can still read it, but you can no longer select, search or copy it, and screen readers cannot read it. Links and form fields are also lost.

Use it for:

• scanned paperwork, receipts and photographed forms
• image-heavy files where only the appearance matters
• documents you only need someone to look at or print

Choosing resolution and quality

For strong mode, choose a Resolution and JPEG quality:

• About 150 DPI is clear on screen and fine for most office printing of text.
• About 100 DPI is enough for reading on a phone or laptop but looks soft when printed.
• 200 DPI or more is better for small print, fine diagrams or anything that will be printed carefully.

Start with medium quality. If the text looks fuzzy, step the resolution up before you raise quality – resolution matters more for sharp letters. Convert to greyscale saves extra space on black-and-white documents and often makes scans look cleaner.

A practical routine

1. Try lossless first. If the result is under your target, you are done, with nothing lost.
2. If it is still too big and the PDF is a scan or photo-based, use strong mode at 150 DPI, medium quality. Check the result by zooming to 100%.
3. If text is unclear, raise the resolution; if the file is still too big, lower the quality one step or switch to greyscale.
4. Still too big? Split it. Split PDF can extract page ranges so you can send the document in two emails, or send only the pages that matter.

Fix the problem at the source

Often the best compression is not creating a huge PDF in the first place:

• Scanning: choose 200–300 DPI and greyscale or black-and-white for text documents. Colour at 600 DPI is rarely needed.
• Photos to PDF: shrink the photos before combining them. Compress Image can reduce each photo to a sensible size, then Images to PDF puts them together.
• Word and other office apps: use “Save as PDF” with the option for smaller file size or “minimum size” where available, and compress pictures in the document first.

When not to compress

• Signed PDFs. If a PDF carries a digital signature, any change – including lossless rewriting – invalidates the signature. Send the original or use a file-sharing link.
• Print-ready artwork. Commercial printers need full-resolution images. Use a transfer service instead.
• Legal or archival originals. Keep the original file and send a compressed copy.

Alternatives to attachments

If the file must stay large, upload it to a cloud drive and email a link. Set the sharing to “anyone with the link” only if the content is not sensitive, and consider Protect PDF to add a password before sharing.

Privacy

Many online compressors upload your document to their servers. Compress PDF on this site runs entirely in your browser: the file is processed on your own device and is never sent anywhere, which matters for payslips, ID scans and medical documents.

Quick reference

• Need selectable text? Lossless.
• Scanned or photo PDF over the limit? Strong, 150 DPI, medium quality.
• Text fuzzy? Raise DPI. Still too big? Greyscale or split.
• Aim for under 10 MB, ideally a few MB, for reliable delivery.