Files with the ASD extension are documents created by Microsoft Word, the word processor included in Microsoft Office. They're used as temporary backups and are automatically created by Word every time a new document is opened. In case the application crashes or is closed unexpectedly, users can recover their unsaved documents using the ASD file.

Just like normal Microsoft Word documents, ASD files can contain various elements such as images, drawn objects, tables, links to websites and links to other local files. The text formatting options and styles of the original document are also preserved.

Microsoft Word's default directories for saving ASD files are:
User\AppData\Roaming\Microsoft\Word - Windows 7, 8 or Vista
User\Application Data\Microsoft\Word - Windows XP

The ASD file format was introduced with Word 7.x and is used with all versions up to and including Word 2007. With the release of Word 2010 it was replaced by the WBK format which is also used in Word 2013.

How to open ASD files

Following a crash or an unexpected system error, backup files are automatically displayed by Microsoft Word when running it for the first time. Saved documents can be selected from the panel on the left.
ASD files can also be opened manually by right clicking them, selecting the "Open With" option and selecting Microsoft Word or by simply dragging and dropping them into the application.