What is a .pdf file?
Portable Document Format · Document · Adobe · 1993
PDF is the universal format for documents that must look identical everywhere. It locks in fonts, layout and images so a file prints and displays the same on any device, which is why it dominates contracts, forms and manuals.
What is a .pdf file used for?
A PDF captures a document as a fixed page layout, embedding the fonts and images it needs. Open it on any phone, computer or printer and it looks the same.
PDFs can hold selectable text, scanned images, form fields, digital signatures and even attachments, which is why they suit everything from invoices to legal filings.
The trade off is that editing a PDF is harder than editing a word processor file. For heavy edits, people export a fresh PDF from the source document.
How to open a .pdf file
The .pdf format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .pdf file.
Windows
- Edge
- Adobe Reader
- any browser
macOS
- Preview
- Safari
- Adobe Reader
Linux
- Evince
- Okular
- Firefox
Web
- Every browser
How to convert a .pdf file
You can convert a .pdf file to DOCX, JPG, PNG, TXT using a conversion tool or the export menu of an app that opens it.
.pdf file signature (magic bytes)
Programs recognise a .pdf file by the bytes at the start of the file, not by its name. These are the signatures for PDF. For a full breakdown, see the PDF file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 25 50 44 46 2D | 0 | '%PDF-' |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .pdf file?
PDF is the universal format for documents that must look identical everywhere. It locks in fonts, layout and images so a file prints and displays the same on any device, which is why it dominates contracts, forms and manuals.
How do I edit a PDF?
Use a PDF editor like Acrobat, or convert it to DOCX, edit in Word, and export back to PDF. Simple text tweaks are possible in many browsers and readers.
Are PDFs safe to open?
Generally yes, but they can carry embedded scripts. Keep your reader updated and be cautious with PDFs from unknown sources.