This article is from the Apple ][ Emulator Resources Guide, by Alex Maddison with numerous contributions by others.
This image is 143388 bytes in size, and is a proprietary format used solely by the Apple II Emulator for Windows. According to the "Apple II Emulator for Windows" help file this format adds a file header separated from the data section of the disk-image by two bytes with value 26 (1Ah). This binary format is used to store non copy-protected images. This format is used solely by the Apple II Emulator for Windows, and is recognised by a .A4W extension. Since no FTP sites store disk-images in A4W format, there is currently no need for a program to convert A4W back to DO or NDO formats.
On the MACINTOSH - There is currently no way to convert either from or to A4W on the Macintosh.
On the PC - Follow the instructions under the 'Disk II Diskette File Format' heading in the "Apple II Emulator for Windows" help file.