.pdf File Extension

What kind of file is a .pdf?

A .pdf file is a Portable Document Format document. It normally uses the application/pdf MIME type and preserves a page's intended layout across devices. One file can contain text, fonts, vector graphics, photographs, forms, annotations, links, metadata, and attachments.¹

PDF files begin with the ASCII characters %PDF-, followed by a version such as %PDF-1.7 or %PDF-2.0. The first five bytes are 25 50 44 46 2D in hexadecimal.¹ Checking this header helps distinguish a PDF from an unrelated file with a misleading name, but a viewer must still validate the rest of the document.

How do I open a .pdf on my computer?

Current desktop browsers can open ordinary PDFs directly. On Windows, use Microsoft Edge, Adobe Acrobat Reader, or another browser. On macOS, double-click the file to open it in Preview, or use Acrobat. Apple documents page thumbnails, text search, annotations, signatures, and other PDF tools in Preview.² On Linux, Firefox, Chromium, and desktop readers such as Okular or Evince are common choices. Standard file and browser apps also display PDFs on iOS and Android.

A browser is usually enough for reading and printing. Try a dedicated PDF application when a complex form, digital signature, attachment, or print-production feature behaves differently.

Poly support for .pdf

Poly renders PDF pages for an in-app preview, extracts available document text and metadata, and applies OCR to image-only pages. Search can find embedded or recognized text and visually similar pages, then jump to the relevant page. The Poly agent can use both extracted text and page images, which helps preserve context from diagrams, tables, stamps, and layout.

OCR is not infallible. Check critical names, totals, and dates against the rendered page, especially in low-resolution, rotated, handwritten, or damaged scans.

History of .pdf

Adobe first published the PDF specification in 1993.³ Its goal was reliable, device-independent exchange of final-form documents. PDF 1.7 became ISO 32000-1 in 2008, moving stewardship of the core specification to ISO. PDF 2.0 is standardized as ISO 32000-2.¹

The .pdf suffix is the registered extension for every PDF version. Specialized profiles such as PDF/A for preservation, PDF/X for print production, and PDF/UA for accessibility still normally use .pdf and application/pdf; their conformance is recorded inside the document rather than in a different suffix.¹

Working with .pdf and alternatives

Choose an output based on what must survive:

• Keep PDF for fixed-layout reading, printing, signing, or sharing.
• Convert to Word or another editable format when revision matters more than exact pagination. Complex columns, fonts, and forms may need repair.
• Export pages to PNG or JPEG for fixed images. This removes selectable text and document structure unless you preserve them separately.
• Extract to plain text or Markdown for lightweight reuse, while checking reading order, tables, and footnotes.
• Use PDF/A for an archival workflow, and validate conformance rather than assuming a normal PDF qualifies.⁴

PDF can contain scripts, links, attachments, forms, and actions, so treat unexpected files as active documents. Keep your viewer updated and avoid approving unfamiliar prompts. RFC 8118 recommends isolating scripts and executable content from untrusted PDFs.¹ Also inspect metadata before publishing, because author and workflow details can travel with the file.