PDF versions explained (1.0 to 2.0)

Every PDF declares a version — 1.4, 1.7, 2.0 and so on. The number tells a reader which features it may need to support, but for most documents the differences are invisible.

A quick timeline

• 1.3–1.4: transparency, layers, and the widely-supported baseline still used today.
• 1.5–1.7: object streams (smaller files), better forms, and the version most tools default to.
• 2.0 (ISO 32000-2): modern encryption (AES-256), improved tagging for accessibility, and cleaner metadata.

Do you need the newest version?

Usually not. A 1.7 PDF opens in virtually everything. Reach for 2.0 only when you specifically need strong AES-256 encryption or the latest accessibility features.

Compatibility in practice

Readers are backward-compatible, so a new reader opens old PDFs and old readers open new PDFs (ignoring features they do not understand). Problems come from broken files, not version numbers.