qpdf
A command-line tool for inspecting, modifying, encrypting, and repairing PDF files — lighter-weight than Ghostscript and ideal for structure-only operations.
qpdf is a focused, content-preserving PDF manipulation tool. Unlike Ghostscript — which re-renders PDFs through a full PostScript interpreter — qpdf works at the structural level, modifying the PDF's object tree directly without touching the visual content. That makes qpdf lighter, faster, and more predictable for operations that don't require rendering.
What qpdf is good at
- Encryption and decryption — add or remove a password, change encryption strength, manage permissions
- Linearization — optimize a PDF for fast web viewing (progressive download)
- Object stream manipulation — compress or decompress internal structures
- Repair — fix broken cross-reference tables and recover damaged files
- QA / inspection — print the object tree and verify structural validity
How PDF Genie uses qpdf
Several of our security-related tools delegate to qpdf:
- Protect PDF — applies AES-256 encryption
- Unlock PDF — strips owner-password restrictions
- Repair PDF — rebuilds damaged cross-reference tables
qpdf vs Ghostscript
They solve different problems:
- qpdf is a scalpel — it makes structural changes without re-rendering, preserving the original content exactly
- Ghostscript is a full PostScript interpreter that can re-render, compress, and convert — useful when you want to change visual output
For a clean password-removal operation, qpdf is the right tool. For aggressive compression that re-renders images, Ghostscript is. Both are free, both are mature.