Methodology

Every tool runs as JavaScript and WebAssembly inside your browser tab. When you add a file, the browser reads it into memory on your device, the tool makes the change there, and the result is offered as a download. The file is not sent to a PDFToolz server.

Most tool pages include a privacy receipt that lists the network requests the page made after you added a file, read from your browser's own timing records. OCR is the one tool that downloads extra code: the Tesseract.js engine and its language data come from the jsDelivr CDN the first time you use it. Your file is not part of that request.

The only data the site stores on a server is what you send through the contact form. See the privacy policy for analytics and hosting logs.

• pdf-lib with fontkit to create and change PDF structure: pages, stamps, form fields and embedded fonts
• PDF.js (Mozilla) to render pages, draw previews and read text
• qpdf, compiled to WebAssembly, for encryption, unlocking and repair
• Tesseract.js for OCR on scanned pages
• docx to write Word files, and fflate for ZIP archives and the zipped Office formats
• React-PDF to lay out resumes in the resume builder

Where no suitable library exists, such as finding blank pages, planning size-based splits or laying out booklets, the logic is our own code.

The parts of each tool that make decisions, such as page range parsing, split plans, page geometry, compression targets and file format readers, are covered by automated tests. Most tools also show a live preview of the result, so you can check it before you download.

File size limits depend on your device. There is no server cap, so the practical limit is the memory your browser can use. Very large files can be slow or fail on phones.

When a page states a figure that comes from someone else, such as an email provider's attachment limit or a value from a file format standard, we check it against a first-party source: the provider's own help pages, the standards body or the published specification. The page then lists those sources and the date they were checked. If we cannot confirm a figure with a first-party source, we leave it out or label it as an estimate.

Every tool and guide page shows the date it was last reviewed. A page is reviewed again when the tool behind it changes, when a cited source changes, and when a reader reports a problem. Notable changes are listed in the changelog.

Spotted something wrong? Use the "Report an error" link on any tool or guide page, or contact us directly.