A PDF that is too big to email is one of life's small annoyances. The good news is that most oversized PDFs are large for a few predictable reasons, and you can usually cut the size dramatically without visible damage.
Why PDFs get big
- Images: photos and scans dominate the file size. A 300 dpi color scan of an A4 page can be several megabytes.
- Embedded fonts: each font family adds size, especially large ones with many glyphs.
- Uncompressed or duplicated content: some exporters store the same image or resource repeatedly.
- Metadata and edit history: incremental saves can leave old versions of objects inside the file.
What compression actually does
Compression tools typically combine several techniques: downsampling images to a lower resolution, re-encoding them at a lower JPEG quality, removing unused objects and metadata, and rewriting the file structure more efficiently. Downsampling and recompressing are lossy, so they trade a little detail for a much smaller file. Cleaning up structure is lossless.
Choosing a target
- Email or web viewing: images around 96 to 150 dpi are usually fine on screen.
- Standard printing: aim for about 300 dpi, which is where most photos look sharp on paper.
- Text-only documents: they are rarely large; if one is, look for embedded images or fonts.
- Scanned documents: run OCR-aware or black-and-white scanning at 200 to 300 dpi, since color scans of text are wasteful.
- 1Make a copy of the original so you can go back if the result looks too soft.
- 2Compress, then zoom in on a page with small text or a photo to check legibility.
- 3If it is still too large, compress more or split the document into parts.
- 4Compress once only; repeated compression stacks up quality loss.
Ways to shrink a PDF before you export it
- Resize photos before placing them in the document instead of after.
- Export from your design or word-processing tool with a 'web' or 'minimum size' preset.
- Avoid embedding many font weights you don't use.
- Scan in grayscale or black and white when color isn't needed.
Frequently asked questions
+Why is my PDF so large?
Usually because of high-resolution images or scans. Embedded fonts and leftover edit data can add to it.
+Does compressing a PDF reduce quality?
Image downsampling and recompression are lossy, so quality drops a little. Structural cleanup is lossless. Check the result before sending.
+What is a good size for an emailed PDF?
Many email providers cap attachments around 20 to 25 MB, but staying under a few megabytes is friendlier to recipients.
+Can I compress a PDF without uploading it?
Yes, with a browser-based compressor that processes the file locally, which keeps sensitive documents private.
Compress PDF
Free, runs in your browser — nothing you enter is uploaded.