In version 1 chart files have a file extension of '.knit'. Version 1 files can be opened in version 3. They are opened in compatibility mode only. This means that they can be viewed and charts and output text can be exported from them. However, while edits to the .knit file are possible, these are discouraged and the saving of any edits is disabled.
In order to edit a version 1 chart file it should first be converted to the version 2/3 format. This is done using the Save As... command. This creates a copy of the original file but in version 2/3 format and with a '.knt2' file extension. The original chart file is not changed.