Format Odyssey

FILE FORMAT GUIDE

PDF File: What It Is & How to Open It

A PDF file describes a paginated document using numbered objects, streams, cross-reference information and a trailer. It can also contain forms, attachments or interactive features.

Compare the reviewed PDF header signature with the filename in your browser.

Check supported file headers

Quick facts

Extension
.pdf
Format
Portable Document Format
Category
document
MIME type
application/pdf
Standard / developer
ISO / Adobe
Open with
Microsoft Edge, Preview, Adobe Acrobat

What is PDF?

PDF begins with a version header containing %PDF-. Readers locate document structures beyond that prefix; a matching header alone does not prove the file is complete, safe or standards-conforming.

How to open PDF

Use a current PDF reader for ordinary viewing. Password protection, damaged files, unsupported form types or interactive content can affect what a reader displays.

Microsoft EdgeWindows / macOS

Double-click the PDF if Edge is your default reader, or choose Open with → Microsoft Edge. Edge can view local PDFs and provides search, zoom, rotation and basic annotation tools.

PreviewmacOS

Double-click the PDF to open it in Preview, or Control-click the file and choose Open With → Preview.

Adobe AcrobatWindows / macOS

Open Acrobat and choose Open, or double-click the PDF after setting Acrobat as the default application. A PDF link may also open directly in a web browser.

Common uses and compatibility

  • Exchange a fixed-layout document across applications and platforms

Things to check

  • PDF content can be encrypted or contain interactive features and attachments; metadata inspection is not a safe-content verdict.

Advanced inspection

These developer and command-line workflows inspect structure or metadata. They are not the default way most people open the file.

pypdf PdfReaderCommand-line tool or library

Construct PdfReader("document.pdf", strict=True) and inspect page count or metadata without writing the file. Handle encryption and parser errors explicitly; successful parsing is not a security scan.

Technical details

Signature
25 50 44 46 2D (%PDF-)
Encoding
Not applicable
Container
PDF object and stream structure
Compression
Not reviewed

PDF Reference and ISO references

Related formats

  • XML Paper Specification Document

    Both represent paginated documents, but XPS uses an OPC-based package and a different fixed-layout specification.

  • EPUB Publication

    EPUB packages publication resources for reading systems and may reflow, unlike a typical fixed-layout PDF workflow.

  • Markdown Text — Markdown scope

    Markdown stores editable plain-text source; producing PDF requires a renderer or export workflow.

Sources & review

Sources reviewed 2026-09-19.