Why is my PDF so large?

The five usual suspects

• Scanned pages: every page is a photograph, so a 20-page scan is 20 photos in a wrapper.
• High-resolution images: photos placed at print resolution when the file will only ever be viewed on screen.
• Embedded fonts: a document using many typefaces embeds a copy of each, sometimes several megabytes' worth.
• Export settings: design tools default to print-ready output with bleed, marks and uncompressed images.
• Hidden extras: attachments, form data, editing history and thumbnail previews all add weight.

A ten-second diagnosis

Ask one question: does the document contain photographs or scanned pages? If yes, image compression will fix it — that is where the bulk is. If it is pure text and still huge, the cause is fonts or export settings, and re-exporting from the source application at screen quality usually beats compressing.

Matching the fix to the cause

• Scans and photos → compress the PDF; expect 60-90% savings.
• Bloated export → re-export at screen/web quality from Word, InDesign or Canva.
• Long document where only part is needed → extract or split instead of shrinking.
• Already compressed and still big → it is genuinely a lot of pages; split it.

Step by step

1. 1Open the PDF and note whether the pages are text or photographs/scans.
2. 2For image-heavy files, run them through the compressor below at medium.
3. 3For text-only files, re-export from the original app at a lower quality setting.
4. 4If only some pages are needed, extract those instead of shrinking the whole file.
5. 5Compare before and after sizes to confirm the fix worked.

Frequently asked questions

Why is my one-page PDF 10 MB?

Almost always a single high-resolution photo or a page scanned in colour at high DPI. Compress it and expect a dramatic reduction.

Can a PDF get bigger when I compress it?

Yes, if it was already optimised — re-encoding adds overhead. The tool reports both sizes, so keep the original if that happens.