An MSO file extension is one that is created when a document is saved as a Web page in the Microsoft Office 2010 application. A file with an MSO extension contains information about object linking and embedding objects contained in the original file. The created Web page may reference the MSO file as a style sheet.
A file extension is a three-character word that comes after the last dot in a file name. It helps to identify the type of file so that the operating system can quickly choose the appropriate application to open the file.
In addition to saved Web pages in Microsoft Office 2010, an MSO file can also be created as an inline email attachment. This happens when a user sends an email message as a Microsoft Word 2000 attachment in Microsoft Outlook. An “oledata.mso” file is attached to the email message so that users who are not using Microsoft Outlook can view the message correctly.
The contents of an MSO file are typically encoded and therefore unreadable if opened using text editors or word processors other than Microsoft Outlook. There are several other applications that can open MSO files or convert them into readable formats when opened in text editors.