How to Reduce a PDF File Size for Email and Upload Forms

By Thiago · Updated September 25, 2026 · 2 min read

Job portals, government forms and email services often cap attachments at 2, 5, 10 or 25 MB, and a scanned document can blow past that with just a few pages. Most of that weight can go away, as long as you know where it comes from.

Why some PDFs are so big

Text in a PDF is tiny: a 50-page report with only text often weighs well under 1 MB. The weight comes from images:

• Scans, where every page is a photo of the paper.
• PDFs made from phone photos, which can be 12 megapixels per page.
• Presentations and catalogs full of high-resolution pictures.

That is why compression works so well on those files and hardly at all on text-only PDFs.

How PDF compression works

ConvertKiwi's Compress PDF uses Ghostscript, the same free engine many professional tools rely on. It lowers the resolution of the images inside the PDF to a target level and re-compresses them, while text and vector graphics stay exactly as they are, so letters remain sharp at any zoom.

In our tests, a 5.9 MB PDF made from phone photos went down to about 290 KB on Recommended, with photos still clear and small text still sharp. If a file would not get smaller, you get the original back, so you never end up with a bigger file.

Step by step

1. Open Compress PDF and add your file (up to 100 MB).
2. Start with Recommended.
3. Download the result and check its size. Open it and zoom in on the smallest text to make sure it is still readable.
4. Still too big? Try Strong on the original file (not on the already compressed one).

When a PDF is still too big

• Send fewer pages. If the form asks for one document, Split PDF can extract just the pages that matter, for example leaving out blank backs of pages or an appendix.
• Rescan at a lower resolution. 150 to 200 dpi is plenty for documents. Many scanners default to 300 or 600.
• Scan in grayscale when color is not needed. It is usually a fraction of the size.
• Compress the photos before making the PDF. If you build the PDF from phone pictures, run them through the image compressor first, then use JPG to PDF.

Things to know

• Password-protected PDFs cannot be compressed. Open the file in your PDF reader with the password and save a copy without protection first, if you are allowed to.
• Signed documents: compressing a PDF that has a digital signature changes the file, so the signature is no longer valid. Compress before signing, or keep the signed original.
• Forms with fillable fields may be flattened by compression. Fill them in first.