A save with Create PDF Compatible File unchecked is unreadable outside Illustrator — that single checkbox causes most ‘AI file won’t open’ tickets. That is the short version; the rest of this page is what we tell people who send us one.
| Extension | .ai |
| Signature | %PDF- or %!PS-Adobe at offset 0 |
| Full name | Adobe Illustrator Artwork |
| Usual MIME type | application/illustrator |
Inside the header
AI files are PDF-based since Illustrator 9, or EPS-based in older saves; the artwork stream is followed by an Illustrator-private data section.
Renaming a .ai file to .pdf usually opens it in any PDF reader, because the file *is* a valid PDF until Illustrator appends its private data.
Recognising the format
The format announces itself in plain text: %PDF- or %!PS-Adobe near the start of the file. If that string is missing, whatever produced the file is not what the extension claims.
A file that was moved through a cloud sync or an email gateway often survives intact and only the name is damaged. Read the header before you believe the name.
Programs that open it
Installed options: Adobe Illustrator, CorelDRAW (import), Inkscape (import), Affinity Designer, Adobe Reader (flattened view). None of them have to be the program that made the file: Universal Viewer reads it and writes nothing back.
Converting .ai to something usable
The targets people actually ask for are .pdf, .eps, .svg, .png, .jpg. Each one has its own page with the settings that matter: ai → pdf, ai → eps, ai → svg, ai → png, ai → jpg
Asked often
Can I convert .ai without the original program?
For the targets listed above, yes. The container survives; what is lost is whatever the target format cannot hold.
What opens .ai if I do not have Adobe?
Adobe Illustrator, CorelDRAW (import), Inkscape (import). If nothing installed reads it, the viewer above does.
How do I know a .ai file is real?
The format announces itself in plain text: %PDF- or %!PS-Adobe near the start of the file. If that string is missing, whatever produced the file is not what the extension claims.
Notes from the file library
Files of this kind are catalogued with the family named in the table above. The family groups them by what a file carries, not by the application that wrote it, which is why two extensions from the same application can sit in different families.
Two things decide whether a file can be opened on a machine that never had the application that made it: the header, which says what the container is, and the structure behind it, which says whether the contents can be read at all. The conversion guides listed on the page cover the targets that come up most often.
Format pages are rebuilt with each release of the toolset, and the review line at the bottom of the page is when an editor last checked the entry against a file. If a page disagrees with a file you have, send the first sixteen bytes and the build number to the support address and the entry is corrected in the next build.
Reviewed 2026-10-05 by M. Halvorsen.