PDF vs PDF/A vs PDF/X vs Tagged PDF

One name, four very different files

When somebody hands you a .pdf, you actually have no idea what is inside. PDF is a container defined by ISO 32000. Inside that container you can have a thin, web-friendly document, a heavyweight print master, a strict archival record, or a screen-reader-friendly accessible document. The file extension is the same; the rules each variant enforces are not.

PDF/A — for archives that need to open in 2060

PDF/A is standardised as ISO 19005. It exists because a regular PDF can quietly depend on fonts installed on your machine, encrypted streams, JavaScript, audio, video, or external links — anything of which can rot or refuse to render decades from now. PDF/A removes all of that. Fonts must be embedded. Colour must be device-independent. Encryption, scripts, and external references are banned.

Pick PDF/A for legal contracts, tax records, medical files, anything that has to be readable long after the software that created it is gone. The common conformance levels are PDF/A-1b (basic visual fidelity), PDF/A-2 (adds JPEG2000 and layers), and PDF/A-3 (allows embedded source files like the original spreadsheet).

PDF/X — for the print shop

PDF/X is ISO 15930. It is what commercial printers want when you send artwork. The constraints exist so a press operator never has to guess: all fonts embedded, all images at the right resolution, a defined output colour intent, and crucially no transparency in PDF/X-1a (transparency is flattened so older RIPs do not produce surprises). PDF/X-4 is the modern variant that does keep live transparency.

Tagged PDF — for screen readers

A regular PDF is a bag of glyphs positioned on a page. A screen reader staring at that has no idea what is a heading, what is a column, or what reading order to use. Tagged PDF adds a parallel tree of semantic tags —<H1>, <P>, <Figure>, <Table> — plus alt text for images and explicit reading order. It is required for WCAG and Section 508 compliance, and baked into the PDF/UA standard (ISO 14289).

Which one do you actually need?

• Sending a contract to a counterparty? Plain PDF is fine.
• Storing it for seven years of statutory retention? PDF/A.
• Mailing artwork to a printer? Ask which PDF/X profile they want.
• Publishing a public document a government will audit for accessibility? Tagged PDF / PDF/UA.

Most consumer PDF tools emit plain PDF by default. If you need a specific variant you usually have to ask for it explicitly in the export dialog. You can merge, compress, or edit PDFs with Toolkiya directly in your browser — nothing is uploaded — but conformance to a specific PDF/A or PDF/X profile depends on how the original file was authored.