Quick answer
- Open Compress PDF and add your file.
- Choose Strong compression and tick Convert images to grayscale.
- Check the result size. Still too big? Remove pages you don't need with Split PDF, then compress again.
- Zoom to 100% and make sure the smallest text is still readable before you upload.
That ladder gets most one to three-page scans under 200 KB, and many under 100 KB. The rest of this guide explains why it works and what to do when it doesn't.
Why size limits exist, and what they're really asking for
Visa centres, university admissions, job portals, courts and government services set limits like 100 KB, 200 KB, 500 KB or 2 MB per file. They store millions of documents, so small files matter to them. What they actually need is a document a human reviewer can read. A file that meets the limit but is too blurry to read will still be rejected, sometimes weeks later.
So the goal isn't the smallest possible file. It's the smallest file that's still clearly legible.
Where the kilobytes come from
| Content | Typical size | What compression can do |
|---|---|---|
| Text exported from Word or Google Docs | 20–100 KB per page | Very little; it's already efficient |
| Phone photo of a page | 1–5 MB per page | Shrink it by 90% or more |
| Scanner output at 300–600 DPI colour | 0.5–3 MB per page | Shrink it by 80–95% |
| Embedded fonts | 20–300 KB per file | A little, through subsetting |
If your PDF is a text document exported from Word and it's already 150 KB, compression won't cut it in half. If it's a scan, you have a lot of room.
The step-by-step ladder
Work down this list and stop as soon as you're under the limit. Each step costs a little quality, so don't go further than you need to.
Step 1: Recommended compression
This lowers image resolution to around 150 DPI equivalent, which looks sharp on any screen. It typically cuts a phone scan from 3 MB to 200–400 KB per page.
Step 2: Strong compression
This goes further, to roughly 100 DPI equivalent with stronger JPEG compression. Printed text in a scan is usually still readable, but check fine print such as passport numbers and dates.
Step 3: Grayscale
A colour image stores three channels of information; grayscale stores one. For documents, colour rarely matters, so grayscale is often the single biggest saving after resolution. Keep colour only if the portal asks for it, for example for photographs or coloured stamps.
Step 4: Fewer pages
If a portal wants proof of address, it probably needs one page of your bank statement, not all six. Use Split PDF with Extract pages to keep only what's needed.
Step 5: Rescan at a lower resolution
If you control the scan, set the scanner or app to 150 DPI, grayscale. Starting from a sensible scan beats compressing a huge one, because there's less detail to throw away.
Size targets by page count
These are realistic targets for scanned A4 or Letter pages after Strong compression in grayscale:
| Limit | Pages that usually fit |
|---|---|
| 100 KB | 1 page, sometimes 2 |
| 200 KB | 2–3 pages |
| 500 KB | 5–8 pages |
| 1 MB | 10–15 pages |
| 2 MB | 25+ pages |
Busy pages, such as forms with fine lines, backgrounds or photos, need more space than plain typed letters.
Common situations
Passport or ID scan for a visa application. Photograph the page flat in daylight, crop to the edges, convert with JPG to PDF (tick Make the PDF smaller), then compress. Keep colour if the guidance asks for a colour copy.
Degree certificate and transcripts for university. Certificates often have coloured seals. Try Recommended compression in colour first; switch to grayscale only if you must.
CV for a job portal. Export from Word as PDF; it's usually already under 200 KB. If it isn't, it's probably a large photo or image in the document. Replace it with a smaller version in Word and export again. Don't scan a CV, because applicant tracking systems need real text.
Several documents, one upload slot. Merge them first, then compress the merged file, so the limit is spread across all the pages.
Mistakes to avoid
- Screenshotting the PDF to make it smaller. It turns text into an image and often makes the file bigger.
- Compressing the same file over and over. Each round of JPEG compression adds blur. Go back to the original and use a stronger setting instead.
- Uploading ID documents to a random website. Check where your file goes. PDFWisely processes files in your browser and never receives them.
- Not checking the result. Open it, zoom to 100%, and read the smallest line before submitting.
Frequently asked questions
Can every PDF be compressed to 100 KB?
Not every PDF. A one or two-page scan usually can. A long, photo-heavy document may not reach 100 KB while staying readable, so you may need to remove pages or split the file.
Why is my scanned PDF so large?
Phone and scanner images are often saved at 300–600 DPI in full colour, which is far more detail than a screen needs. Lowering the resolution and switching to grayscale removes most of the size.
Will compressing make the text blurry?
Text in a normal PDF isn't affected. In a scan, the text is part of the image, so strong compression can soften it. Always zoom to 100% and check the smallest text before you submit.
Is it safe to compress ID documents online?
Only if you trust the service. PDFWisely compresses files inside your browser, so passports and statements never leave your device.