Practical guide | Reproducible synthetic test
PDF too large for email? Reduce it methodically
Measure the file, try lossless optimisation first and use high compression only when you can accept pages converted to images.
Synthetic test with 4 image-heavy pages
Original PDF
22.5 MB
High compression
0.9 MB
Measured reduction: 96%
22.5 MB became 0.9 MB, a measured reduction of 96%. This deliberately image-heavy fixture is not a promise for every PDF.
Before you start
Check the real limit before compressing
Attachment limits vary by email provider and often apply to the whole message, not just the PDF. Attachment encoding can also increase the transmitted size. Check your provider’s current limit and consider a protected sharing link if the document is still too large.
Measured evidence
The test you can reproduce
We generated a four-page A4 PDF from synthetic PNG images, without customer documents or personal information. The same engine used by the editor produced these results:
Original
22.5 MB
4 synthetic pages with large images
Lossless
22.5 MB
No useful reduction, so the editor keeps the original
High compression
0.9 MB
Pages converted to JPEG images, 96% smaller
Results vary with the images, page count and any existing compression. A mainly text-based PDF may shrink far less.
A reliable five-step method
- 1
Measure the original file
Note its size before making changes and keep a separate copy.
- 2
Try lossless optimisation
This keeps selectable text, links and forms. If it does not produce a smaller file, the editor keeps the previous version.
- 3
Download and inspect it
Open the copy and check every page, especially images, signatures, links and fillable fields.
- 4
Use high compression only when needed
This mode rasterises every page as a JPEG. The file may become much smaller, but interactive features are lost.
- 5
Check before sending
Confirm the final size, legibility and completeness. If it is still too large, use a protected link rather than compressing it again.
Choose the right mode
Lossless optimisation
- Keeps native text selectable.
- Preserves links, form fields and document structure.
- May not reduce a PDF that is already optimised.
High compression
- Converts every page to a JPEG image.
- Removes selectable text, links and fillable fields.
- May reduce sharpness and print quality.
Check before attaching the PDF
- The file is below your email provider’s limit.
- Every page is present and readable.
- Links and forms work if they need to be retained.
- The original document is stored separately.
Important limitations
- A specific final file size cannot be guaranteed.
- High compression is unsuitable when people need to copy text, fill in forms or use links.
- Compressing or editing a digitally signed PDF may invalidate its existing signature.
- Compression does not securely remove confidential information and is not a substitute for verified redaction.
Frequently asked questions
- Can every PDF be reduced below 1 MB?
- No. The result depends on the content and existing compression. The editor keeps the previous version when the new file is not smaller.
- Will the quality remain identical?
- Yes with lossless optimisation. High compression uses JPEG images and may reduce sharpness and print quality.
- Is my PDF uploaded to a server?
- The document content is processed in your browser memory. The hosting service may still receive ordinary technical visit data, as described in the privacy notice.
- What if the PDF is still too large?
- Avoid further quality loss. Consider a protected sharing link and check who can open it and for how long.