Why Is My PDF So Big? 7 Reasons and How to Fix Each One

Oct 24, 2026 · 3 min read · Documents

You scan a single page and the PDF is 8 MB. You export a short report from Word and it will not attach to an email. PDF size surprises almost everyone, but the causes are few and each has a simple fix.

1. It is made of photos

A scanned PDF is a photo of every page. A phone camera photo is several megabytes, so a five-page scan can easily be 20 MB.

Fix: use Compress PDF in Recommended mode, which re-saves the scanned pages as smaller JPGs. Start with the High level; Strong mode can go even smaller.

2. The scan resolution is too high

Scanner apps and office scanners often default to 300 or even 600 DPI. That is useful for printing photos, but 150 DPI is enough to read a document on screen.

Fix: set your scanner to 150 DPI next time, or compress the existing file at 110 or 150 DPI.

3. Colour where grey would do

A colour scan stores three times as much information as a greyscale one, and an off-white page full of slight colour noise compresses badly.

Fix: use your scanner app's "document" or "black and white" mode for text pages. The paper becomes pure white, which takes almost no space.

4. Large pictures inside a Word or PowerPoint file

If you pasted full-size phone photos into a document, the PDF keeps every pixel even if the picture is shown small on the page.

Fix: compress the pictures before you add them, using the image compressor with a max width of about 1600 pixels. In Word you can also use the "Compress Pictures" option before exporting.

5. Embedded fonts

A PDF can carry the full font files it uses, so it looks the same everywhere. Unusual or decorative fonts can add a few hundred kilobytes each.

Fix: stick to common fonts, or choose the option to embed only the characters used ("subset") when you export.

6. Blank or unneeded pages

Scanning both sides of every page adds blank backs. Each blank scan still costs space, because the paper texture is stored as an image.

Fix: remove them with Delete PDF pages, or keep only the pages you need with Extract PDF pages.

7. Leftover data from editing

Some programs keep old versions, hidden layers or form data inside the file after edits.

Fix: try Compress PDF in Recommended mode, which rebuilds the file structure, shrinks pictures and keeps the text selectable.

How small can a PDF be?

As a rough guide, a text-only page made from Word is 20 to 100 KB. A well-compressed scanned page that is still easy to read is 50 to 150 KB. If your pages are much bigger than that, one of the reasons above applies. For forms with a strict limit, see our guide to reducing a PDF to under 100 KB or 200 KB.

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