Guides

Short, practical explanations for the jobs our tools do.

• Which PDF tool do I need?A quick decision guide for common PDF jobs: combining files, taking pages out, reordering, shrinking for email, converting to images and adding or removing passwords.
• Image formats, dimensions and quality — explainedWhy some images are huge and others blurry: formats, pixel dimensions, DPI, quality settings and cropping, with practical sizes for web, email and print.
• What "processed in your browser" really meansHow in-browser tools work, what local processing protects against, what it does not, and how to check for yourself that a tool does not upload your files.
• How to test PDF compression qualityA practical method to compare PDF compression levels: what to check (text, images, links, forms, print), and how to pick the smallest file that still works.
• Cron, time zones and daylight saving timeWhy cron jobs run at unexpected times: server time zones, daylight saving gaps and repeats, UTC in the cloud, and practical rules to schedule reliably.
• chmod: the same bits mean different things on files and directoriesWhy 644 suits files and 755 suits directories, what execute means on a folder, how to fix permissions recursively without making everything executable.
• Decoding a JWT is not verifying itAnyone can decode a JSON Web Token. Learn what signature verification proves, which claims to check, and common JWT mistakes that lead to security holes.