A PDF can be large for several different reasons, and the right fix depends on the cause. Here are five practical ways to reduce file size, and when each one helps.
1. Downsample embedded images
The biggest wins usually come from images. Reducing their resolution and re-compressing them can cut a file by 70–90% with little visible difference at normal viewing sizes.
2. Re-save with efficient compression
Even text-only PDFs can shrink a little when re-saved with modern stream compression that removes redundancy. This is lossless — nothing is degraded.
3. Remove pages you don't need
If you only need to share two pages of a 50-page document, extract just those pages. It's the simplest size reduction of all.
4. Scan smarter
If you control the scan, use 150 DPI and grayscale for documents. This produces far smaller files than 600 DPI colour, with no real loss for text documents.
5. Strip metadata and extras
Author info, thumbnails, and revision history add weight. A good optimizer removes these automatically.
Step by step
- Identify the cause first: select text on a page to tell a scan from a text PDF.
- Remove pages you do not need — the fastest saving available.
- Convert to grayscale if it is a colour scan.
- Compress to a target size, in one pass, from the original file.
What usually goes wrong
Compressing before removing pages wastes effort
You spend quality on pages you were going to delete. Trim first, compress once.
Metadata and hidden content are rarely the problem
It is a real saving on a small file and a rounding error on a large one. Look at the images first.
A file that will not shrink is telling you something
If a PDF resists compression, it is usually already compressed, or it is a scan at its floor. Change the input rather than the setting.
Frequently asked questions
Which method shrinks the file most?
For image-heavy or scanned PDFs, downsampling the images wins by far. For text PDFs, removing pages or re-saving is the main lever.
What makes the biggest difference to PDF size?
The embedded images. Text costs kilobytes; a single full-resolution photograph costs megabytes.
In what order should I apply these steps?
Remove unneeded pages, convert to grayscale if it is a colour scan, then compress once to your target.