PDF — Portable Document Format
PDF (Portable Document Format) is a document format created by Adobe in 1993 and now an open ISO standard (ISO 32000). Its defining feature is fixed layout: a PDF describes exactly where every character, line and image sits on the page, so the document renders identically on any device, operating system or printer.
A PDF can contain text, fonts, vector graphics, images, forms, annotations and digital signatures — everything needed to reproduce a finished document faithfully.
What PDF files are used for
- Sharing final documents: contracts, invoices, CVs, reports and official letters
- Print-ready files — what you see is what prints
- Forms that need to be filled in and signed
- Long-term archiving (the PDF/A variant is designed for it)
- E-books, manuals and datasheets
Advantages
- Renders identically everywhere — no font or layout surprises
- Opens on effectively every device, including in every web browser
- Supports digital signatures and password protection
- Compact for text-heavy documents
Limitations
- Difficult to edit — PDFs are designed as final output, not working documents
- Extracting content (text, tables) is lossy and often awkward
- Scanned PDFs contain only images of text, requiring OCR to search or edit
- Complex layouts don't reflow well on small screens
How to open a PDF file
Every modern web browser opens PDFs directly — just drag the file into a browser window. Dedicated readers include Adobe Acrobat Reader, Preview (built into macOS) and countless mobile apps. Editing requires specialised software, which is why converting to an editable format is often the more practical route.
Frequently asked questions
Why won't my PDF file open?
The usual causes are an incomplete download (the file is cut off, so readers report it as damaged), a password the file was saved with, or an outdated reader. Try opening it in a web browser first: drag the file into Chrome, Edge, Firefox or Safari. If the browser can't open it either, the file itself is damaged and the safest fix is to download or request it again.
Can a PDF file contain a virus?
It can. PDFs can carry embedded JavaScript and attachments, and malicious ones exploit bugs in old PDF readers. Opening PDFs in an up-to-date browser or reader, which sandbox the file, removes most of the risk. Be wary of a PDF that asks you to enable content or open an attachment, especially from an unexpected email.
How do I turn a PDF into an editable Word file?
Convert it to DOCX. A text-based PDF (one exported from Word or another app) converts into editable paragraphs in seconds with the PDF to Word converter. A scanned PDF is only a picture of text, so it needs OCR software first.
What is PDF/A?
PDF/A is an ISO-standardized version of PDF built for long-term archiving. It embeds every font and forbids features that depend on outside resources, such as external links to fonts, JavaScript and encryption, so the file still renders the same decades later. Courts, governments and archives often require it.
How do I make a PDF file smaller?
Large PDFs are almost always large because of images: scans saved at high resolution or photos placed at full size. Re-exporting with lower image resolution, or rebuilding the PDF from resized images, shrinks it dramatically. Our guide on why PDFs get so large walks through each cause.