How to reduce PDF file size without losing quality
Updated November 4, 2026 · 6 min read
Email providers commonly cap attachments at 20–25 MB, and job portals, government sites and university systems often allow as little as 2–5 MB. If your PDF is over the limit, the fix is usually quick once you know what is making it big.
What actually makes a PDF large
Text is tiny. A 100-page report of plain text is often well under 1 MB. The weight almost always comes from images:
- Scanned pages. Every page of a scan is a full-page photo. A phone scan at full camera resolution can be 2–5 MB per page.
- Photos and screenshots pasted into a document at their original size, even when they are displayed small.
- Embedded fonts add some size, but rarely more than a few hundred kilobytes.
So the most effective way to shrink a PDF is to make its images smaller, which is exactly what a good compressor does.
1. Compress the images (biggest win)
Compression downscales images that have more pixels than the page can show and re-encodes them as efficient JPEGs. With PDFHeron’s Compress PDF you choose a level:
- Light keeps near-original quality. Good for documents you will print.
- Recommended is the right choice for email and most uploads.
- Strong produces the smallest file for strict size limits.
Text, fonts and vector graphics such as charts are not touched, so they stay sharp and searchable. Scanned and photo-heavy PDFs commonly shrink by 70–90%. And because PDFHeron runs in your browser, the document never leaves your computer.
2. Delete pages you don’t need
Blank scanned backs, cover sheets and appendices nobody asked for all add weight. Open the PDF, select those thumbnails and delete the pages before compressing.
3. Remove images that don’t add anything
Decorative banners, large logos repeated on every page and background photos can be removed individually with the Objects tool. See remove images from a PDF.
4. Split the document
If a portal limits each upload, split the PDF into parts by page range, for example one file per chapter, and upload them separately.
5. Scan smarter next time
For text documents, scanning at 150–200 dpi in grayscale is plenty to read and print. Scanning at 600 dpi in full color produces files many times larger with no visible benefit on screen.
Quick checklist
- Delete unnecessary pages.
- Run Compress PDF on Recommended.
- Still too big? Try Strong, or split the file.
- Open the result and check it is readable before sending.
A note of caution: compression can’t do much for a PDF that is already mostly text. If a 300 KB text document needs to be smaller, it is already about as compact as it can be.