A PDF that is too big to email is nearly always too big because of its pictures: phone photos dropped into a report, or a scanner saving every page as a 300 dpi colour image. Text and fonts are rarely more than a few hundred kilobytes. So the fix is to shrink the images to what a screen can show and leave everything else alone.
Recommended mode shrinks the photos and keeps the text, then shows you the saving.
The limits you are aiming under: Gmail takes 25 MB of attachments on a personal account. Outlook.com caps the whole message at 20 MB, and Microsoft's default for business Exchange accounts is 10 MB. Work and school accounts can set their own, so leave some room.
One command. /ebook brings any image placed sharper than about 225 PPI down
to 150 PPI, which is sharp on any screen and fine on paper:
gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -o small.pdf input.pdf
Install it with brew install ghostscript on a Mac or apt install ghostscript
on Debian and Ubuntu. On a six-page report with a phone photo on every page,
that took the file from 52.7 MB to 328 KB:
-rw-r--r-- 1 root root 52689397 Oct 18 13:57 input.pdf
-rw-r--r-- 1 root root 328080 Oct 18 14:04 small.pdf
Already on a Mac: Preview
macOS ships a filter for this. Open the PDF in Preview, choose File › Export…, set Quartz Filter to Reduce File Size, and save under a new name.
On macOS 26.5 the filter file sets JPEG quality 0.7 and a 144 PPI target. Run through the same filter, the 52.7 MB report came out at 1.1 MB and a six-page 300 dpi scan went from 7.1 MB to 2.9 MB. Text, the link and the form field all survived.
It has no settings you can change from Preview, and it re-encodes every image as JPEG, including screenshots and diagrams that were stored losslessly. Those can come out with smudged edges.
What each route actually changes
All of them shrink the same thing, the images, and none of them turns your text into a picture. Ghostscript and Preview rebuild the whole file around the smaller images, though, and that has side effects. These are the results on the same 52.7 MB report (six pages, 808 words, one link, one form field):
| Route | Image resolution | Size | Text | Form field |
|---|---|---|---|---|
| Original | 602 PPI | 52.7 MB | 808 words | Kept |
gs /screen |
72 PPI | 125 KB | 808 words | Dropped |
gs /ebook |
151 PPI | 328 KB | 808 words | Dropped |
gs /printer |
301 PPI | 3.0 MB | 808 words | Dropped |
| Preview, Reduce File Size | 144 PPI | 1.1 MB | 808 words | Kept |
qpdf, lossless |
602 PPI | 52.7 MB | 808 words | Kept |
Ghostscript 10.05.1 removed the fillable field with every preset. It also
converted the images to an ICC colour space with /printer. If the PDF is a
form somebody has to fill in, don't send it through Ghostscript.
The lossless row is there to show what "compress without losing anything" is worth on a file like this:
qpdf --object-streams=generate --compress-streams=y --recompress-flate --linearize input.pdf small.pdf
It saved 1.9 KB out of 52.7 MB. Repacking the structure helps a PDF that was saved badly, and does almost nothing to one that is big because of its photos. The browser tool's Lossless mode runs this same qpdf pass.
pdfimages -list (from poppler) shows every image with the resolution it is
placed at. Run it before and after to see what changed:
pdfimages -list small.pdf
page num type width height color comp bpc enc interp object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
1 0 image 1008 756 rgb 3 8 jpeg no 9 0 151 151 50.8K 2.3%
2 1 image 1008 756 rgb 3 8 jpeg no 19 0 151 151 52.7K 2.4%
The x-ppi column is the one that matters. 150 is plenty for reading. Above
300 is detail nobody will see in an email.
In the browser
- Open Compress PDF and drop the file in. It shows the page count and the size.
- Leave Recommended selected. It shrinks the images and keeps the text selectable, the links working and the form fields fillable.
- Pick eBook for a document people will read on screen. If it is still over the limit, try Screen.
- Press Compress PDF. The result line shows the size before and after, and how many images were recompressed.
- Press Download. The file is saved with
-compressedadded to its name.
Recommended only touches an image that is placed at more than one and a half times the target resolution, which is the convention Acrobat uses. It downsamples it, saves it as JPEG, and leaves everything it can't safely decode exactly as it was. If the result is no smaller than the original, you get the original back.
Scans
A scanned page is one picture, so a scan is all images, and the same 150 PPI
target works. The six-page colour scan above went from 7.1 MB to 896 KB with
gs /ebook, and to 293 KB with /screen.
Black-and-white office scans are often saved as JBIG2 or CCITT, which are already very small. Recommended leaves those alone and will say so: "No compressible images found", or a low count of images recompressed. That is the case for Maximum.
Maximum renders every page as an image, and warns you before you run it.
Maximum renders each page as a JPEG (110 DPI at eBook) and builds a new PDF from the pictures. It gives the smallest file, but text can no longer be selected or searched, and links and form fields are gone. For a plain scan there was no text to lose. For a scan that has been OCR'd, there was: keep Recommended, or the original.
Every route here except qpdf throws image detail away for good. Save the compressed copy under a new name and compress from the original if you need to try again. Compressing a compressed copy loses detail twice.
If it is locked
If the PDF asks for a password to open it, no compressor can read it until the password is removed. Remove it first (you need to know it), then compress.
If it is still too big after all of this, the PDF is the wrong way to send it. Gmail already turns attachments over 25 MB into a Google Drive link. A shared link from any cloud drive does the same job without shrinking anything.
