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PDF explained

The PDF format, PDF/A, OCR, scanned PDFs, forms, passwords: what they are and how they behave.

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What are PDF annotations?PDF annotations are marks stored in a layer above the page content: highlights, underlines, freehand ink, text boxes, sticky notes, stamps, shapes and links.What are PDF forms?A PDF form is a PDF with interactive fields (text boxes, checkboxes, dropdowns, signature slots) that a reader can fill in and save.What are PDF passwords and permissions?PDF passwords come in two kinds: an open (user) password that encrypts the file so nobody can read it without the key, and an owner (permissions) password that leaves the file readable but asks readers to block printing, copying or editing.What is OCR?OCR, optical character recognition, is software that looks at an image of a page and works out which letters and words are in it.What is PDF/A?PDF/A is a restricted form of PDF defined by ISO 19005 for long-term archiving: everything needed to display the page must be inside the file, and features that could change or break over time are forbidden.What is a PDF file?A PDF file (Portable Document Format) is a document that stores page layout, text, fonts and images in one package so it looks the same on any screen or printer.What is a scanned PDF?A scanned PDF is a file in which every page is an image, usually produced by a scanner, a copier or a phone camera app, with no text underneath.