How to shrink a PDF for an upload portal.
Without making it unreadable.
Most oversized PDFs are large because of images: scanned pages or photos of documents. Re-rendering those pages at a lower resolution (around 100–150 DPI) is usually enough to get under a 1–2 MB portal limit with pages that are still easy to read. The trade-off is that re-rendered pages become images, so text can no longer be selected or searched. If the portal accepts several files, splitting the PDF or removing unneeded pages is often the better first step.
Why is the PDF so big?
- Scans are often made at 300–600 DPI in colour. Each page is a large photo.
- Phone photos of receipts or documents placed in a PDF keep their full camera resolution.
- Text-only PDFs exported from Word are usually small already; if one is large, embedded images are the likely cause.
Choose an approach
| Approach | Keeps selectable text | Good when |
|---|---|---|
| Remove pages you don’t need | Yes | Only part of the document is required |
| Split into several PDFs | Yes | The portal allows more than one file |
| Optimize (for example Adobe Acrobat’s Compress PDF) | Yes | You have the software and the PDF is mostly text |
| Re-render pages at a lower DPI | No | The PDF is scanned or photo-based, or nothing else gets under the limit |
On a Mac, Preview’s File → Export → Quartz Filter → Reduce File Size also shrinks PDFs, but it often reduces images so much that pages become hard to read. Check the result.
PDF Stack removes, reorders or extracts pages into a new PDF, and Image Fit re-renders a PDF to a KB limit. Both run in your browser without uploading the file.
Which resolution to choose
| DPI | Use it for |
|---|---|
| 200 | Small print, detailed drawings, or when the limit is generous |
| 150 | Most letters, forms, statements and IDs. A good default. |
| 100 | Tight limits; ordinary text stays readable on screen |
| Below 100 | Only when nothing else fits; zoom in and check every page |
With Image Fit, enter the portal’s limit and a starting DPI. If the file is still too big, the tool lowers JPEG quality and then, if you allow it, the resolution.
When not to re-render a PDF
- Fillable forms: form fields are flattened away. Fill and save the form first, or use an optimizer.
- Digitally signed documents: any rebuild invalidates the signature. Upload the original or ask the recipient for another route.
- Documents someone must search or copy from: the text becomes part of the image.
Check before you submit
Open the smaller PDF at 100% zoom and look at the smallest text, stamps, signatures and any numbers that matter. Keep the original file: re-rendering can’t be undone.
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