Compress PDF

Purpose

Compress a PDF for smaller file size — useful for email attachments and upload-size limits. The strategy is rasterization-based: each page renders as an image and re-embeds, often hitting 10-30% of the original size. Note: text becomes a flat image layer (no longer selectable or searchable) — best for scans or final-distribution copies. Runs locally via pdfjs-dist + pdf-lib; no upload, no watermark, no page limit, free.

Steps

1. Drag or pick a PDF
2. Review the left-side file info: current size, page count, whether a text layer exists
3. Pick a compression level: "Maximum" (smallest, lower quality) / "Balanced" / "High quality" (lightest compression, quality preserved)
4. (Optional) Tune the "Output DPI" between 72 and 200
5. (Optional) Enable "Preserve selectable text layer" (less reduction but keeps search functionality)
6. Review the estimated output size
7. Click "Process"
8. Wait per-page (about 1-3 sec each)
9. Download the compressed file with reduction percentage shown

FAQ

Will text become blurry after compression?

Image-based compression turns text into pixels. "High quality" mode (DPI 200) keeps text readable; "Maximum" mode (DPI 72) has visible blur — only fit for screen preview. To keep text crisp and selectable, enable "Preserve selectable text layer" (size reduction is smaller but functionality stays).

How does this compare to server-side tools like Smallpdf or iLovePDF?

Server-side tools use more sophisticated algorithms (resource dedup, font subsetting, intelligent image compression) — they can achieve smaller output at the same quality. But they require uploading. pdfbox's edge: "the file never leaves your device". If file confidentiality > maximum compression ratio, pick pdfbox.

Can I OCR a compressed PDF to make it searchable again?

Yes. If you compressed in "image-based" mode, the output is essentially a page of images — perfect input for the OCR tool to re-add a searchable text layer.

Will the file be uploaded?

No. pdfjs-dist renders each page locally, pdf-lib reassembles the new PDF locally — no uploads at any stage.

Why do compression rates vary so much between files?

It depends on source content: high-image PDFs compress dramatically (70-90% reduction); pure-text PDFs may even grow after image rasterization (you wouldn't compress those); scans grow or shrink proportional to DPI vs the original scan resolution.

Use cases

• Squeeze a PDF under 25MB for an email attachment
• Compress a large PDF to under 100MB for WeChat transfer
• Save cloud storage space by archiving compressed PDFs
• Get a resume PDF under a 5MB job-site upload limit
• Batch-compress scans before sharing to save bandwidth

Tip

Check the file's makeup first: pure-text PDFs may actually grow when rasterized — convert to Word format instead. High-image PDFs compress most dramatically. To preserve search functionality, pick "Preserve selectable text layer" + "Balanced" mode.