Question 1

Why should I compress a PDF?

Accepted Answer

Compressed PDFs are easier to email (many services have 10–25 MB attachment limits), faster to upload to cloud storage and web forms, and consume less disk space. Compression is especially valuable for scanned documents and image-heavy reports.

Question 2

Why does compression work better for image PDFs than text PDFs?

Accepted Answer

This tool compresses by re-rendering pages to JPEG images at lower quality. Image-heavy PDFs shrink significantly because their content is already pixel-based. Text-based PDFs store text as scalable vectors — rasterising them to JPEG can actually increase size or reduce quality without meaningful savings.

Question 3

Is JPEG compression lossy? Will quality degrade?

Accepted Answer

Yes, JPEG compression is lossy. Lower quality settings introduce visible artefacts, especially around sharp text and fine lines. For archiving or printing, use high quality (92). For email or web sharing, medium (80) is usually sufficient.

Question 4

What does DPI mean and how does it affect compression?

Accepted Answer

DPI (dots per inch) controls how many pixels are used per inch when rendering each page. Lower DPI means fewer pixels and smaller file size. 72 DPI is suitable for screen-only viewing; 96 DPI is a good balance; 150 DPI is recommended for print-quality output.

Question 5

When should I use 72 DPI versus 150 DPI?

Accepted Answer

Use 72 DPI when the PDF will only be viewed on screen (websites, previews, email previews). Use 96 DPI for general sharing. Use 150 DPI when the recipient needs to print the document clearly without purchasing a high-quality original.

Question 6

Can I compress a PDF/A file?

Accepted Answer

Technically yes, but the output will no longer conform to PDF/A standards since the re-rendering process removes embedded metadata and ICC profiles required for archival compliance. Do not compress PDF/A files that must remain archive-compliant.

Question 7

What is the maximum compression I can achieve?

Accepted Answer

For scanned PDFs with many full-page images, compression ratios of 60–80% reduction are common at low quality + 72 DPI. Text-only PDFs may see little or no reduction, and can occasionally be slightly larger due to JPEG artefacts in text areas.

Question 8

What happens if I compress an already-compressed PDF?

Accepted Answer

Re-compressing a JPEG-heavy PDF degrades quality further with minimal size savings — each compression cycle multiplies JPEG artefacts. It is best to always compress from the original uncompressed source, not from a previously compressed version.

PDF 압축기

PDF 압축이란?