How to Reduce PDF File Size Before Emailing or Uploading

Last updated: July 2026

A PDF that refuses to attach to an email, fails a government portal's upload limit, or takes minutes to send on mobile data almost always has the same root cause: it contains images that are far larger than they need to be. This guide explains why PDFs balloon in size, how to prevent it at the source, and how to shrink files you already have.

Why Is My PDF So Large?

A PDF made from typed text is tiny. A ten-page contract exported from Word is usually under 200 KB, because text in a PDF is stored as characters plus font information — extremely compact. Size problems come from three places:

• Scans. A scanned page is a photograph of paper. At 600 dpi in colour, one A4 page can be 5–10 MB. Twenty pages of that and you have a 150 MB file for what is, in substance, a few thousand words.
• Phone photos inserted as pages. Modern phone cameras produce 12–50 megapixel images. Dropping them straight into a PDF embeds the full-resolution photo even though it will only ever be viewed at screen size.
• Embedded fonts and duplicated resources. Less common, but documents assembled from many sources sometimes embed the same font or image repeatedly.

Fix It at the Source: Scan Settings That Matter

The cheapest compression is the scan you never inflate in the first place. If you control the scanner or scanning app, three settings determine almost everything:

A 300 dpi black-and-white scan of an A4 page is typically 50–100 KB. That is a 50–100× improvement over a colour photo of the same page, with better legibility.

Shrinking a PDF You Already Have

Option 1: "Print to PDF" at reduced quality

Every modern operating system includes a virtual PDF printer. Open the large PDF, choose Print, select "Save as PDF" (or "Microsoft Print to PDF" on Windows), and pick a lower quality setting if offered. This re-renders each page and often cuts scanned files by 60–80%. The trade-off is that any text layer produced by OCR is lost — the output is purely visual.

Option 2: Built-in compression in PDF readers

Many free PDF readers and office suites include a "Reduce file size" or "Optimize PDF" function. LibreOffice (free) can open a PDF via Draw and re-export it with JPEG compression set to 70–80% quality, which is visually indistinguishable for documents.

Option 3: Downsample the images before creating the PDF

If your workflow is "photograph pages with a phone, then convert to PDF", resize the photos first. Reducing a 4000×3000 photo to 1600×1200 keeps text perfectly readable and cuts the size by around 85%. Most phone gallery apps can resize on share, and scanning apps like the built-in document scanners in iOS Notes and Google Drive already do this for you — prefer them over the plain camera.

What About Upload Limits on Government Portals?

Tax, GST, court e-filing, visa, and university portals commonly cap uploads at 1–5 MB per file. The reliable recipe for meeting these limits:

1. Scan (or rescan) at 200 dpi, black and white.
2. Combine the pages into a single PDF in the correct order — you can merge the PDFs in your browser so the documents never leave your device.
3. If still over the limit, run the merged file through a "print to PDF" pass at reduced quality.
4. Open the result and confirm every page is legible before uploading — a rejected filing costs far more time than a careful check.

When Not to Compress

Some documents should keep their full quality: signed originals that may be needed as legal evidence, engineering drawings, medical imaging, and anything where fine detail matters. For these, keep a full-quality archive copy and compress only the copy you transmit. Compression is lossy — you cannot restore detail that has been thrown away.