COM Add-ins vs. Application-Specific Add-ins
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In the previous and current versions of Microsoft® Word, Microsoft® Excel, Microsoft® Access, and Microsoft® PowerPoint®, you can use Microsoft® Visual Basic® for Applications (VBA) to create add-ins specific to each of those applications. For example, you can create an add-in for Word that builds a custom report from a selected database and another add-in for Excel that performs a similar task. You save the Word add-in as a Word template file (*.dot), and the Excel add-in as an Excel add-in file (*.xla). Despite the fact that the add-ins share common code, you have to create separate add-ins to add functionality to both applications.
Note Microsoft® Outlook® and Microsoft® FrontPage® do not provide any way to create application-specific add-ins by using VBA.
A COM add-in, on the other hand, can share some add-in functionality and code across applications. The COM Add-in project contains a component for each application in which it will run and is registered for each application. Usually, a COM add-in contains some code that is common across all applications and some that is specific to each application. For example, if you build a COM add-in to create a custom report in Word or Excel from a database, the code that accesses the database and retrieves a set of data can be shared. When you have retrieved the data, you must work with the Word object model to write the data to Word and with the Excel object model to write the data to Excel.
The following table lists both types of add-ins and their file extensions.
| Add-ins | File extensions | Available to |
|---|---|---|
| Word add-ins (application-specific) | .dot, .wll, .wiz | Word only |
| Excel add-ins (application-specific) | .xla, .xll | Excel only |
| PowerPoint add-ins (application-specific) | .ppa, .pwz | PowerPoint only |
| Access add-ins (application-specific) | .mda, .mde | Access only |
| Exchange Client extensions (application-specific) | .dll | Outlook and Microsoft® Exchange clients only |
| COM add-ins | .dll | Word, Excel, Access, PowerPoint, Outlook, and FrontPage |
COM add-ins and application-specific add-ins also differ in terms of how the user views and installs available add-ins. In all Microsoft® Office XP applications, the COM Add-Ins dialog box displays the available COM add-ins.
See Also
Add-ins, Templates, Wizards, and Libraries | What Is a COM Add-in? | Viewing the List of Available COM Add-ins | Viewing Available Application-Specific Add-ins