Compress PDF to 1 MB — shrink phone scans privately

How to use Compress PDF to 1 MB

1. Choose the PDF from your files. On a phone this can be the PDF your scanner app saved. The target is preset to 1 MB, shown as 1024 KB.
2. Leave If needed, convert pages to images to reach the size ticked.
3. Tick Black and white for printed documents without colour; leave it off for photos, stamps or coloured forms.
4. Tap Compress to 1 MB and keep the page open while the progress bar runs.
5. Check the new size, look through the preview, then download the file ending in -1mb.pdf.

What it does and when to use it

One megabyte is a frequent cap for documents that run longer than a page or two: an admission form with attachments, a visa supporting document, a medical report for an insurance claim, a signed offer letter returned to HR. It is roomy for digital PDFs and fairly comfortable for scans, as long as the scan was not made at extreme settings.

The usual problem is the phone scanner. Scanner apps produce attractive, high-resolution colour pages, and a ten-page document can come out at many megabytes, sometimes far more. Most portals reject it outright. This tool brings such files down to 1 MB or just under, keeping as much detail as that budget allows.

How it works

The work is done in your browser. The PDF is not uploaded, and nothing is stored once you close the page.

If the file is already at or below 1,000,000 bytes, you get it back unchanged. If not, the tool repacks it losslessly with pdf-lib and qpdf and keeps that version if it fits. A scan rarely fits this way, because nearly all of its size is the page photos.

The next step redraws every page with pdf.js and saves it as a JPEG in a fresh PDF. The search starts at 150 DPI, which for an A4 page means about 1240 × 1754 pixels, a resolution at which ordinary printed text reads comfortably. It tries JPEG quality between 35% and 85%, and lowers the resolution (120, 100, 85 DPI and below) only when the lowest quality is still too big. The aim is the largest file that fits under 1 MB.

A quick budget guide

Dividing the target by the page count shows how much room each page gets.

These are simple divisions, not measurements. The real outcome depends on how busy each page is: a page of dense small print or a photo needs more bytes than a short letter.

Worked examples

A 12-page scan from a phone app. Each page gets about 83 KB. The tool will usually stay near the higher resolutions with moderate JPEG quality, and the result panel names the exact DPI and quality it used. If any page looks soft, a cleaner rescan of that page helps more than any setting.

A three-page medical report with coloured charts. There is plenty of room per page, so leave Black and white off to keep the chart colours meaningful.

A 40-page document. Each page gets about 25 KB. In black and white that can still be readable for plain text, but check carefully. If the portal accepts several files, splitting the document with the PDF Splitter and compressing each part gives each page more room.

Limits and tips

• Page images replace real text, so the result cannot be searched or copied. Run OCR PDF afterwards if you need that.
• Compressing the same file again does not improve it. Always start from your original.
• Many scanner apps have a quality or size setting. Choosing a medium setting at scan time gives this tool a better starting point.
• Fixed presets instead of a target are available in the PDF Compressor. For a 2 MB limit, use Compress PDF to 2 MB.