Compress a PDF so it fits as an email attachment

Almost all of the weight in a large PDF is images: photos, scanned pages, screenshots, and logos placed at print resolution. The text takes almost no space, so the tool works on images: it decodes each embedded JPEG, scales it down if its longest edge is above the ceiling for your level, re-encodes it at a lower quality, and puts it back, then saves the file with object streams so unused objects and duplicated structure are dropped.

A few things are deliberately left alone. Images under 16 KB are skipped because re-encoding them saves nothing. Flate-compressed images, CMYK JPEGs, indexed-color images, and the transparency masks attached to other images are not touched, because pushing them through the browser canvas would shift their colors or corrupt the mask. If a re-encoded image would not come out at least 5 percent smaller, the original is kept.

Under Compression level there are four cards. Balanced is selected by default and labeled the usual choice for email: images are capped at 1,600 pixels on the longest edge at a moderate JPEG quality, which is plenty for reading on a screen. Light keeps images up to 2,400 pixels at high quality and suits a document someone will print or zoom into; it saves less. Strong drops the ceiling to 1,100 pixels at a lower quality and is the smallest result that still keeps text selectable; photos look softer, but text and layout are unchanged.

Flatten to images renders each page to a JPEG at 120 dpi and builds a new PDF from those pictures. For a scan this is often a large saving, because the scan was probably stored at a much higher resolution. But the result has no text layer: nobody can select, search, or copy from it, and a screen reader cannot read it. A warning appears when you pick it. Do not use it on a contract or form the recipient needs to search or fill in, and not on a text-only PDF: unlike the other three levels, Flatten never hands back your original, so a small text document can come out larger than it went in.

Start with Balanced. If the note under the result still shows a size above the limit your email service publishes, click Start over, add the file again, and try Strong. Reserve Flatten to images for scans.

If the rewritten file is not smaller than the original, the tool hands back your original unchanged and says no saving was possible: it is probably already optimized or has no images to re-encode. This is common for a PDF exported from Word or Google Docs that contains only text and vector graphics, and for files whose images are already small or stored in a format the tool leaves alone.

In that case, change what you send rather than how it is compressed. Split PDF can cut the document into Custom ranges or Fixed size pieces you send in separate emails. Organize PDF lets you delete pages the recipient does not need, such as blank scans or a long appendix. If one page is the whole problem, PDF to JPG can render just that page as a picture to attach on its own, and a shared link from your cloud storage avoids the attachment limit entirely.

The compressed file is named with a -compressed suffix, so it sits next to your original rather than replacing it. Open it and look at a page with a photo or scan. At Strong the softening is visible when you zoom in; decide whether the recipient will mind. Try selecting a line of text to confirm it is still text, unless you chose Flatten to images.

If you compressed several files at once, Download all as ZIP gives you one archive to attach. The files are stored in the ZIP without further compression, since PDFs and JPEGs do not deflate well, so the archive is about the sum of the files and the email limit applies to that total.

Everything runs in your browser and nothing is uploaded. Files up to 100 MB are accepted, and above 50 MB a warning says the file is processed entirely in memory, so it can take a while and may struggle on a phone.