A default document is the file that a web server displays when you browse to a folder without specifying a file name.
This is syntax:
<system.webServer>
<defaultDocument>
<files>
<clear />
<add value="Path of your Page" />
</files>
</defaultDocument>
</system.webServer>
Using IIS 7 you can set default document in Web.Config in easy way. Suppose i have to set CommingSoon.aspx page as default page then we should do like this in system.webserver tag.
<configuration>
<system.webServer>
<defaultDocument>
<files>
<add value="CommingSoon.aspx" />
</files>
</defaultDocument>
</system.webServer>
</configuration>
When IIS gets this new default document it adds with parent or global list of default documents.
To remove an individual default document from the list.
<files>
<remove value="CommingSoon.aspx" />
</files>
To remove a default document entry from the inherited or parent list of default documents, do something like this:
<files>
<clear/>
<add value="CommingSoon.aspx" />
</files>