How to reduce a PDF’s file size for email and upload forms
Why PDF files get large, how to shrink scanned and text documents, and when sending fewer pages is the better fix.
Updated: 3 November 2026
Email providers and online forms often limit the size of attachments, and a PDF that looks small on screen can be surprisingly large. The right way to shrink it depends on what is inside, so start by working out where the size comes from.
Why PDFs get big
Most of a PDF’s size is usually images and embedded fonts. A document exported from a word processor with a few pictures is often modest. A scan is a different story: every page is a full-size photograph of the paper, so a 20-page scan can be tens of megabytes even though it contains very little “data”.
Option 1: shrink scanned or image-heavy PDFs
For scans, the Compress PDF has a strong mode that turns each page into a compressed JPEG image. You choose the resolution and quality, and it shows the new size before you download. As a starting point, 120 DPI at around 70% quality usually keeps a scanned page readable on screen while making the file much smaller; raise either value if text looks soft. The trade-off is important: because each page becomes a picture, text can no longer be selected or searched, links stop working, and screen readers cannot read the document. Always keep your original.
Option 2: lossless mode for text documents
The lossless mode rebuilds the file with a more compact structure and removes unused data, and the text stays selectable. The saving is often modest, because most of the weight is in images that this mode does not recompress. If the result is not smaller, the tool says so and does not offer a bigger file as “compressed”. That usually means the PDF was already efficient.
Option 3: send fewer pages
Sometimes the simplest answer is to send only what is needed. With the Extract or Delete PDF Pages you can keep the pages you need or delete the rest, and the Split PDF can break a long document into parts that each fit under a limit. If you are combining documents, merge them with the Merge PDF first, then compress the combined file once.
Other things that help
- If you made the PDF yourself, export it again with the “minimum size” or “reduce file size” option your software offers, and use smaller images to begin with. The Image Compressor can shrink pictures before you place them in the document.
- If you can scan again, a lower scan resolution (150 to 200 DPI is often enough for reading) makes smaller files than compressing a high-resolution scan afterwards.
- Check the limit you actually have. Email services and upload forms set different maximums, and it is better to know the number than to compress more than you need.
Before you send it
Open the compressed file and zoom in to check that small print, stamps and signatures are still legible. Password-protected or encrypted PDFs are not supported by the tool, so remove the password first with the program that created the file.