что делать:
нажимаем F1 - далее Saving and Exporting Artwork - потом Saving artwork in Illustrator format или Saving artwork in EPS format - там находим - цитата:
{To export artwork to a legacy Illustrator format:
1. Choose File > Export.
2. Type a filename, and choose a location for the file.
3. Choose Legacy Illustrator (*.AI) as the file format, and click Export.
4. In the Illustrator Legacy Options dialog box, select the version of Illustrator with which you want your file to be compatible.
5. Set additional options, and click OK:}