What is an AI file?

AI is a document format, describing pages rather than pixels. It stores shapes and coordinates rather than pixels, so it stays sharp at any size — a logo scaled to a billboard loses nothing. It is used for print, editing and line art and logos.

The extension is .ai, and the full name is Adobe Illustrator Artwork. Both matter less than what the file can hold, which is what the rest of this page is about.

Adobe published it in 1987.

A format that has been readable for that long is a format worth trusting with something you want back in ten years.

Reading it outside the vendor’s own software depends on work done by other people, usually by inspection rather than by documentation. That mostly works and occasionally does not, which is the reason to convert anything you intend to keep.

AI stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.

AI carries an alpha channel, so a logo keeps its soft edges over whatever sits behind it instead of arriving in a white box.

It can work in RGB and CMYK, the model a printing press needs.

CMYK is the one that decides whether a printer accepts the file, and it is the thing most often lost converting to a screen format.

AI is not limited to one page, which matters when converting to something that is: one conversion produces one file holding a single page — the first one, unless the page is something the converter lets you pick.

AI stores the parts of an image separately rather than flattened together, which is what makes it a working file. Almost every format it converts into flattens them, and the flattening is not reversible — keep the layered original.

Adobe Illustrator reads it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

AI is meant to be opened and changed. Keep the file in this format for as long as the work is going on, and export from it whenever a finished copy is needed.

The recurring complaints: support outside its home ground is uneven.

None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.

Since Illustrator 9 in 2000, saving an `.ai` with the Create PDF Compatible File option enabled produces a file that is a valid PDF. The option is on by default and most designers never change it. So the file a designer sent you can very often be opened by copying it, renaming the copy to `.pdf`, and double-clicking.

This is the single most useful thing to know about the format and it is rarely said outright. What you get is the artwork as it looked when saved — accurate, printable, viewable in anything that reads PDF. What you do not get is the editable structure, which is the point of the next section.

A PDF-compatible `.ai` contains the drawing twice. There is the PDF stream, which any reader can render, and alongside it Illustrator’s private data holding layers, editable paths, appearance settings, effects, artboards and the history of how the artwork was constructed.

That is why the files are large, and why turning the compatibility option off roughly halves the size. It is also why the rename trick shows you the picture and not the project: PDF readers see the PDF half and ignore the rest, which is exactly what the arrangement was designed for.

Edit it as the designer would. Opening the PDF representation in another vector editor gives you paths, but the layer structure, live effects, appearance stacks, symbols and text on a path have all been flattened into whatever produced the visible result.

Some editors — Inkscape, Affinity Designer, CorelDRAW — read the PDF half well enough for real work, and that is the practical route for someone who needs to make a change and has no Illustrator. Expect to rebuild anything clever rather than to inherit it.

An `.ai` may embed its fonts or merely name them. Where they are named and the machine lacks the typeface, something else is substituted and the letter widths change — which in a logo means the wordmark is simply wrong, and it is the kind of wrong that survives until it is printed.

The long-standing defence is converting text to outlines before handing the file over, turning every letter into a shape. It guarantees appearance and makes the text permanently uneditable. For a logo delivered to a printer that is correct; for a file the client will need to update, it is a problem handed forward, and both versions are worth keeping.

Illustrator files built for print are usually CMYK and often carry named spot inks — a specific Pantone the brand is printed in. Converting to any screen format maps those into RGB, and some cannot be represented.

The visible effect concentrates on saturated cyans, deep blues and strong oranges, which come out slightly duller. Nothing has gone wrong. Send the original to the printer and treat the converted copy as the version people look at, rather than trying to make one file serve both.

Illustrator files can contain several artboards — separate canvases in one document, used for a logo in its variants, a set of icons, or every size of an advertisement.

Converted to PDF these become pages, and converted to a raster format most tools take only the first. If a conversion produces one image where you expected six, this is why. Opening the renamed PDF is the quickest way to see how many artboards a file actually holds before deciding how to convert it.

Adobe has never published the `.ai` format. Everything other software knows about it comes from the PDF half, which is documented, plus reverse engineering of the rest. That is why support outside Adobe’s own tools ranges from good to absent with little in between.

It is the same shape of problem as camera raw: a private format read by inference. The difference is that the PDF compatibility layer gives everyone a documented path to the artwork, which is a considerably better position than raw formats are in.

Files from before Illustrator 9 are not PDF-compatible, because the feature did not exist. Those are PostScript-based and behave like EPS — renaming them to `.pdf` produces an error, and reading them needs software that understands the older structure.

Illustrator itself opens them, as do some vector editors. If a file predates 2000 and nothing modern will read it, that is the explanation rather than damage, and converting it is a job for a tool with genuine legacy support rather than a general-purpose converter.

SVG for the web — vector like the original, sharp at any size, and rendered directly by every browser. This is the right destination for a logo going onto a website. PDF for print or for sending onward, which loses nothing because it is already half of what the file contains.

PNG at a generous size for placing into a document or a presentation, where scaling does not matter. Keep the `.ai` in every case: it is the only version that still holds the layers, the artboards and the editable construction, and no conversion recovers them.