PDF (.pdf)
Portable Document Format — the universal standard for shareable, print-ready documents.
- Extension
- MIME Type
- application/pdf
Last updated
What Is a PDF File?
PDF (Portable Document Format) was developed by Adobe in 1993 and became an open ISO standard (ISO 32000) in 2008. It is designed to present documents consistently across all devices, operating systems, and software — a PDF looks identical whether opened on Windows, macOS, iOS, Android, or a web browser.
What Does a PDF Contain?
A PDF is a structured binary file containing:
- Text streams — compressed sequences of characters linked to embedded font definitions
- Raster images — JPEG, PNG, or TIFF data embedded directly inside the file
- Vector graphics — mathematical curve definitions for logos, charts, and diagrams
- Fonts — full or subsetted font files embedded for consistent rendering
- Metadata — title, author, creation date, and keyword tags
- Cross-reference table (xref) — an internal directory mapping every object to its byte offset
Common PDF Problems
| Problem | Cause | Fix |
|---|---|---|
| "File is damaged and cannot be repaired" | Missing or broken xref table | Use Repair PDF tool |
| File too large to email | High-DPI embedded images | Use Compress PDF tool |
| Pages sideways or upside-down | Scanner orientation error | Use Rotate PDF tool |
| Text not selectable | Scanned image-only PDF | Requires OCR processing |
PDF Versions
| Version | Year | Key Feature Added |
|---|---|---|
| PDF 1.0 | 1993 | Basic text and images |
| PDF 1.4 | 2001 | Transparency and layers |
| PDF 1.7 | 2006 | 3D content, digital signatures |
| PDF 2.0 | 2017 | Improved encryption, page-level output intent |
MIME Type
application/pdf — the IANA-registered MIME type for PDF files. Used by web servers to signal that a response contains a PDF, triggering the browser's built-in PDF viewer.
Tools for PDF files
- Compress PDF
Compress PDF files online to reduce file size without losing visual quality. Optimises images and streams — free, private, runs entirely in your browser.
- JPG to PDF
Convert one or more JPG images to a PDF document online. Combine multiple photos into a single PDF in seconds — free and private.
- Merge PDF
Merge multiple PDF files into one online document. Drag to reorder pages, combine in seconds — free, private, browser-based.
- PDF to JPG
Convert PDF pages to high-quality JPG images online. Each page becomes a separate JPG — free, private, browser-based.
- Repair PDF
Repair corrupted or damaged PDF files online. Recovers unreadable documents and fixes structure errors — free, private, no upload required, runs in your browser.
- Rotate PDF
Rotate PDF pages 90, 180, or 270 degrees online. The fix is permanent — not a viewer preference. Free and browser-based.
Related terms
Related terms
- Cross-Reference Table (xref)
The internal index inside a PDF file that maps object numbers to their byte positions — the most common point of PDF corruption.
- OCR (Optical Character Recognition)
Technology that extracts machine-readable text from scanned images or image-based PDFs, making content searchable and selectable.