If a PDF is surprisingly large, there's almost always a specific culprit. Knowing which one tells you exactly how to fix it.
High-resolution images
The most common cause. Photos and screenshots placed at full resolution, or scans at high DPI, dominate the file size. Downsampling them is the fix.
It's a scan
If the whole document is scanned, every page is an image — see our scanned-PDF guide for the specific approach.
Embedded fonts
Fully embedded fonts add weight. Subsetting (embedding only the used characters) helps, though this is usually a smaller factor than images.
Leftover junk
Old revisions, thumbnails, and metadata accumulate. Re-saving through an optimizer clears these out.
Step by step
- Try to select text on a page. If you cannot, it is a scan and that is your answer.
- If it is a text PDF, look for full-resolution photographs and screenshots.
- Compress to a target, or convert to grayscale first if it is a colour scan.
- Remove pages you do not need — often the quickest single saving.
What usually goes wrong
It is almost always the images
Text costs kilobytes. A single phone photograph placed in a document costs megabytes. One picture usually explains the whole file.
Embedded fonts add up on short documents
A full font can add a megabyte. That barely registers in a 200-page report and dominates a two-page letter.
Editing history and deleted content can persist
Some editors keep prior versions inside the file. A re-save through a different tool often drops them.
Frequently asked questions
My PDF is only text but still large — why?
It may contain fully embedded fonts or accumulated revision data. A lossless re-save usually trims it.
Why is my scanned PDF so much bigger than a typed one?
Because it is a photograph of every page rather than text. A page of text is a few kilobytes; a scan of the same page is hundreds.
What is the fastest way to reduce PDF size?
Compress to a target size. If it is a colour scan, convert to grayscale first — that alone often removes a third.