What is a PDF file?
Updated October 12, 2026
PDF (Portable Document Format) is a file format for documents that need to look the same everywhere. Adobe introduced it in 1993, and since 2008 it has been an open international standard (ISO 32000). Today, every computer, phone and web browser can open a PDF without extra software.
What a PDF holds
A PDF describes each page exactly: where every letter, line and image goes. To make that work on any device, a PDF usually includes the fonts it uses. A PDF can also contain:
- Links, bookmarks and a table of contents
- Fillable form fields and digital signatures
- Scanned pages as images, sometimes with a hidden text layer from OCR so you can search them
- A password that's needed to open the file, or that restricts printing and editing
Why PDFs are hard to edit
A PDF stores the finished layout, not the document's structure. It knows that a word sits at a particular spot on page 3, but not always which paragraph that word belongs to. That's great for printing and sharing, and it's why editing text in a PDF is harder than in a Word document. Page-level changes, such as combining, splitting, rotating and reordering pages, are easy and lossless.
Everyday PDF tasks
| Task | Tool |
|---|---|
| Combine several PDFs into one | Merge PDF |
| Pull pages out into separate files | Split PDF |
| Rotate, delete or reorder pages | Organize PDF |
| Turn a Word document into a PDF | Word to PDF |
| Comment, highlight or fill in forms | PDF editor |
All of these run in your browser, so your documents aren't uploaded.