Learning centre
Practical, plain-English guides to working with PDF files. We write about the questions people ask us most: why files are large, how to keep documents private, what makes a PDF accessible, and how signatures work.
- What is a PDF? How the format works and why it lastsA plain-English guide to the Portable Document Format: what is inside a PDF file, why it looks the same everywhere, and the PDF/A and PDF/UA variants.7 min read · Updated 24 October 2026
- Why are some PDFs so large? A guide to PDF file sizeWhat makes a PDF big, what compression can and cannot do, and practical ways to get a document under an email or upload limit.8 min read · Updated 24 October 2026
- Making accessible PDFs: a practical checklistHow screen readers use tagged PDFs, why scanned documents are a problem, and the checks to run before you publish a PDF for the public.8 min read · Updated 24 October 2026
- PDF privacy: what your documents reveal and how to protect themHidden metadata, fake redaction, password strength and the difference between uploading a file and processing it in your browser.9 min read · Updated 24 October 2026
- PDF page sizes explained: A4, Letter, points and DPIHow PDF measures pages, the dimensions of common paper sizes, and how to avoid printing problems when documents cross the Atlantic.6 min read · Updated 24 October 2026
- How to scan documents to PDF with your phoneGetting clean, readable scans from a phone camera, choosing between JPG and PNG, and combining pages into a single PDF that is easy to send.6 min read · Updated 24 October 2026
- Electronic signatures and digital signatures: what is the difference?A clear explanation of typed, drawn and certificate-based signatures, what each one proves, and when you might need more than a picture of your signature.7 min read · Updated 24 October 2026
- How to combine PDF files on Windows, Mac, iPhone and AndroidStep-by-step ways to merge PDFs on any device, using built-in apps where they exist and a free browser tool where they don’t.6 min read · Updated 25 October 2026
- How to sign a PDF without printing itSign PDFs on a computer, iPhone or Android phone using built-in features or a free browser tool, plus tips for a signature that looks right.6 min read · Updated 25 October 2026
- How to password protect a PDF (and remove a password)Add a password to a PDF on Windows, Mac or in your browser, choose one that is actually secure, and unlock a PDF when you know the password.6 min read · Updated 25 October 2026