Every PDF term you'll ever need, explained in plain English.
Every PDF term you'll ever need, explained in plain English.
PDF is one of the oldest file formats still in heavy daily use — its first version shipped in 1993 — and three decades of evolution has produced a vocabulary that's intimidating from outside. Terms like AcroForm, PDF/A, OCR, AES-256, redaction, Z-order and 'flatten' get used freely in tutorials and tool UIs without explanation. This glossary defines them in plain English.
Use the search box to jump to a definition. Each entry starts with a one-line plain-English summary, then a paragraph of detail. Internal links point you to the relevant PDFWix tool when one exists — for example, the AES-256 entry links to Protect PDF, the OCR entry links to our OCR explainer.
If we missed a term you needed, email contact@pdfwix.com — we add new entries every release.
AcroForm — the original PDF interactive form technology, introduced in PDF 1.2 (1996). AcroForms use form-field objects (text, checkbox, radio, dropdown, signature) embedded in the PDF and read by any modern PDF viewer. They are what most government tax forms, bank applications and HR onboarding documents use. Our Fill PDF Form tool detects AcroForm fields automatically and lets you tab between them like a web form.
PDF/A — an ISO-standardised subset of PDF designed for long-term archiving (PDF/A-1 in 2005, PDF/A-2 in 2011, PDF/A-3 in 2012, PDF/A-4 in 2020). It forbids features that depend on external resources (live JavaScript, external fonts, encryption) so that the document will still render identically in 50 years. Archives, courts and regulated industries usually require PDF/A for permanent records.
Flattening — the process of permanently baking interactive layers (form values, annotations, signatures, comments, layer visibility) into the underlying page content stream. After flattening, the text and graphics are still selectable but the original form fields and annotation objects are gone. Most PDFWix tools flatten on download so the output renders identically in every viewer, including ones that don't support interactive layers.
Written by the PDFWix team and reviewed for accuracy. We use AI for first-draft suggestions only when we already know the answer — every published entry is reviewed by a human.
Yes. Each term has a unique anchor (e.g. /pdf-glossary#aes-256). Right-click a term to copy the direct link.
We cover the parts of PDF that show up in real-world tools and workflows — PDF 1.3 through PDF 2.0, with notes when behaviour changed between versions.