What is a .ai file?
Adobe Illustrator Artwork · Design · Adobe · 1987
AI is Adobe Illustrator's native vector artwork format. Since Illustrator 9 it is actually a specialised PDF, embedding Illustrator's own editable layer and path data inside a file any PDF viewer can also open, which is why an AI preview shows up correctly almost anywhere even though only Illustrator can truly edit it.
What is a .ai file used for?
A modern AI file is a valid PDF with Illustrator-private data appended, so double-clicking one, or opening it in any PDF reader, shows the artwork correctly. Only Illustrator understands the private data that keeps paths, layers and effects fully editable.
Files saved before Illustrator 9 (2001) predate that PDF compatibility and are instead built on plain PostScript, the same lineage as EPS, which is why an old AI file's header starts with '%!PS-Adobe' rather than '%PDF-'.
Because Adobe has never published the format's full internal structure, other vector apps such as Inkscape or Affinity Designer can only partially import an AI file, generally by reading the embedded PDF content and losing Illustrator-specific editability like live effects.
AI supports artboards, layers, gradients, and both vector paths and embedded raster images, the same working-file richness that PSD offers for a Photoshop project.
How to open a .ai file
The .ai format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Illustrator
- Inkscape (partial import)
- Photopea (web)
macOS
- Illustrator
- Preview (view only)
- Affinity Designer (partial import)
Linux
- Inkscape (partial import)
- GIMP (raster import only)
Web
- Photopea
How to convert a .ai file
You can convert a .ai file to PDF, SVG, EPS, PNG using a conversion tool or the export menu of an app that opens it.
.ai file signature (magic bytes)
Programs recognise a .ai file by the bytes at the start of the file, not by its name. These are the signatures for AI. For a full breakdown, see the AI file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 25 50 44 46 2D | 0 | '%PDF-' (modern AI, Illustrator 9 and later, is a PDF-compatible file) |
| 25 21 50 53 2D 41 64 6F 62 65 | 0 | '%!PS-Adobe' (legacy AI, before version 9, is PostScript-based) |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .ai file?
AI is Adobe Illustrator's native vector artwork format. Since Illustrator 9 it is actually a specialised PDF, embedding Illustrator's own editable layer and path data inside a file any PDF viewer can also open, which is why an AI preview shows up correctly almost anywhere even though only Illustrator can truly edit it.
Can I open an AI file without Illustrator?
Yes, for viewing: since Illustrator 9, an AI file is a valid PDF, so any PDF reader shows the artwork. For real editing, Inkscape, Affinity Designer or the free web app Photopea can import it, though very complex Illustrator-specific effects may not survive.
Why does my AI file open as a PDF?
It essentially is one. Modern Illustrator saves a complete PDF representation alongside its own private editing data in the same file, which is why PDF software can open it, while only Illustrator can access the layers and paths for editing.
Related formats
Sources
Details on this page were checked against authoritative references: