Introduction
An AI file is the working file of Adobe Illustrator, the vector drawing program. It holds artboards, layers, paths, text, gradients, symbols and any placed images, everything needed to carry on editing.
Early versions of Illustrator saved a form of PostScript. Since Illustrator 9 the default has been a PDF-compatible file, so many programs can show an AI file as a PDF even though only Illustrator can edit it fully.
Structure
A modern AI file is a PDF: it starts with %PDF- and has the usual PDF
objects, pages and cross-reference table, which give a viewable copy of the artwork.
Illustrator's own editing data is stored inside it as additional private streams,
often compressed. That private data is not publicly documented.
Files saved by Illustrator 8 and earlier, or saved without PDF compatibility in old
formats, start with %!PS-Adobe instead and are PostScript with
Illustrator's own comments and procedures.
Links
Software
- Adobe Illustrator (Windows, macOS, iPad)
- Inkscape (Windows, macOS, Linux), imports PDF-compatible files
- Affinity Designer (Windows, macOS, iPad)
- CorelDRAW (Windows, macOS)
- Preview (macOS), shows the PDF part