A lot of Excel procedures are packaged in Add-Ins. An Add-In is basically a workbook containing some code, that has some other unique properties. An add-in usually has some user interface elements, such as buttons on the ribbon or on context (right-click) menus, so you can access its features.
The add-in workbook itself is invisible, though it has one and often more hidden worksheets, where information related to the add-in may be stored. The add-in can be installed, which means it opens every time Excel opens, so that its functionality is always available. An Excel add-in can also be opened like a regular file when you need it, without installing it, though it is still hidden.
Preparing to Install the Add-In
Very often, an Excel add-in is packaged in a zip file. Unzip the file, and store the add-in in the User Add-in Library, which is
where USERNAME is your Windows login. You can get there quickly by pressing Win+R (Win = Windows key), typing %appdata% in the Run box, and clicking OK (which opens the Roaming directory), and drilling down to Microsoft and then AddIns.
You can actually store the add-in in almost any convenient folder, but when you use the Add-In Library, it’s easy to find the add-in from within Excel when you install it.
Windows protects your computer from malicious software that came from a different computer than yours, but it also protects your computer from useful software that comes from my computer, so you need to unblock the add-in. Right click on the add-in file in Windows Explorer, and choose Properties. At the bottom of the General tab of the Properties dialog, there may be a notice that the file may be blocked, and there is a checkbox to unblock the file. (Below is the dialog for Peltier Tech Charts for Excel, my commercial Excel charting add-in.)
Check the Unblock box, and click OK.
Installing the Add-In
If you have the Developer tab showing on Excel’s ribbon, go there and click on Excel Add-Ins (or if it’s an older version of Excel that has no Excel Add-Ins button, click on Add-Ins) to open the Add-Ins dialog.
Otherwise, click on the File tab > Options > Add-Ins. Click the Go button near the bottom of the list to open the Add-Ins dialog.
Or you can use the old Excel 2003 shortcut, Alt+T+I, to open the Add-Ins dialog.
If you stored the add-in in the User Library, it will appear by name in the Add-Ins dialog. Otherwise you will have to click Browse, then navigate to find the add-in.
Check the box in front of this entry, then click OK, and the add-in is installed, available whenever you run Excel.
Uninstalling an Excel Add-In
Follow the steps to get to the Add-Ins dialog (Developer tab > Excel Add-Ins, File tab > Options > Add-Ins > Go, or Alt+T+I). When the Add-Ins dialog opens, locate the add-in in the list, uncheck the box in front of it, and click OK. The add-in should remain in the list, to make it easy to reinstall at some future time.
Using an Excel Add-In without Installing
If you don’t want an Excel add-in installed all the time, you can simply start it when you need it, using File > Open in Excel, double clicking on the add-in file in Windows Explorer, or dragging it from Windows Explorer and dropping it on Excel.
Note that the add-in must be unblocked before opening it in Excel. When a regular workbook is blocked, it will open in Excel in a Protected Mode window, and it cannot be edited. An add-in does not open in a window, so a blocked add-in will simply not load. Follow the steps to unblock the add-in, and it will load just fine.
Install an Excel Add-In in Excel for Mac
The protocol to install an add-in on the Mac are similar. Visit Install an Excel Add-In in Excel for Mac to read the specifics.