What is a PDF file?
PDF stands for Portable Document Format. It is a file format that keeps a document looking exactly the same on every screen and printer — fonts, images, layout and all.
A short history
PDF was introduced in 1993 to share documents between computers that had different software and fonts. In 2008 it became an open international standard (ISO 32000), so anyone can create and read PDF files without paying a licence.
What is inside a PDF
A PDF can contain text, vector drawings, photos, fonts, form fields, links, comments, bookmarks and even digital signatures. Each page is described precisely, which is why a PDF prints the same way everywhere.
- Text PDFs: created from Word, design tools or exports — the text can be searched and selected.
- Scanned PDFs: photos of paper pages — they look like text but are really images.
- Mixed PDFs: scans with an added hidden text layer (OCR) so they can be searched.
Why PDF is everywhere
Contracts, invoices, plans, manuals, résumés and school assignments are shared as PDF because the recipient sees exactly what the sender intended, the file is compact, and it opens on any device without special software.
PDF compared with images and Word files
An image (JPG, PNG) is one flat picture — great for photos, but text inside cannot be edited. A Word file is easy to edit but can look different on another computer. PDF sits in between: it keeps the layout fixed while still holding real text, links and form fields.