Quick answer
Almost always it is the images: phone photos, colour scans at high resolution or screenshots stored without compression. Text and drawings take very little space. To shrink the file, recompress the images — for example with Compress PDF, which keeps text sharp and selectable — or save/scan it again at a lower resolution.
The usual suspects
- Photos from a phone. A single 12-megapixel photo can add 3–6 MB. Ten of them in a report and you are at 50 MB.
- Scanned pages. A scan is a picture of a page. Scanning in colour at 600 dpi makes each page several megabytes, even when it only contains text.
- Screenshots and graphics stored without compression. Some programs embed images as raw pixels.
- Embedded fonts. Usually small, but full fonts with many characters (for example Chinese, Japanese or Korean) can add megabytes.
- Duplicated content. The same logo or background stored again on every page, or PDFs merged many times.
Fix 1: compress the images inside the PDF
Our Compress PDF tool decodes each photo in the PDF, scales it to a sensible size and saves it as an efficient JPEG, while leaving text, fonts and vector drawings untouched. Photo-heavy PDFs often become 50–90% smaller. It runs in your browser, so contracts and statements are never uploaded.
Compress PDF → Shrink PDFs in your browser; text stays sharp and selectable.Fix 2: export it smaller in the first place
- Microsoft Word (Windows): File → Save As → PDF, then under Optimize for choose Minimum size (publishing online).
- Photos in a document: resize them before inserting them — 1600–2000 pixels wide is plenty for a page. Resize Image does this in batches.
- Making a PDF from photos: resize first, then combine them with JPG to PDF.
Fix 3: scan with sensible settings
- Text documents: 150–200 dpi in greyscale or black-and-white is easy to read and small.
- If the text needs to be recognised (OCR): 300 dpi.
- Colour only when colour matters, such as photos, stamps or signatures in blue ink.
Fix 4: split it
Some portals have a strict limit per file (2–10 MB is common). If one file is still too big after compressing, send it in parts with Split PDF, for example one file per chapter or per 10 pages.
How small can it get?
A PDF that is mostly text from Word or a website is usually already small; there is little to gain. Scans and photo-heavy PDFs shrink the most. For the absolute smallest file, the Extreme setting in Compress PDF turns pages into images — but then the text can no longer be selected or searched, so use it only when size matters more.
Frequently asked questions
Why is a scanned PDF so large?
Each scanned page is an image. Colour scans at high resolution are several megabytes per page, even when they only contain text.
Does compressing a PDF reduce quality?
Only the images are recompressed. With sensible settings the difference is hard to see, and text stays sharp.
How do I make a PDF smaller to email?
Compress it, and if it is still above the email limit (often 20–25 MB), split it into parts.
Why did compression barely help?
PDFs that are mostly text, or whose images are already compressed, have little to gain.