IrfanView, a shareware viewer/editor, does not lend itself to the automatic installation of a plug-in using an installer. However, it can use 8BF filters. Here is how to manually install AstroFlat Pro if you are using IrfanView as your image editor.
You must install the IrfanView PlugIns package in order to be able to run AstroFlat Pro. This package is freely downloadable from the same websites from which you can download IrfanView itself. IrfanView's help explains how to download and install the IrfanView PlugIns package.
First, you must open an image to view in IrfanView in your normal manner. You will not be able to access the Adobe 8BF Filters dialog if no image is loaded.
Click on Image in the main menu, then select Adobe 8BF PlugIns in the drop down menu. This will cause a submenu to be displayed. Select the Filter Dialog entry in this submenu to display the IrfanView - Adobe 8BF Filters dialog box.
Note that you can also directly access the IrfanView - Adobe 8BF Filters dialog box by pressing Control K on your keyboard.
Press the [ Add 8BF Filters (Folder) ] button, then navigate to the folder containing the AstroFlat Pro plug-in that is installed on your computer. See Plug-in File Locations for the location of this file. Currently, IrfanView is only available as a 32 bit application so you will want the 32 bit variant of AstroFlat Pro. Select the folder containing the 32 bit file AstroFlatPro.8bf.
Once you have added AstroFlat Pro to the list in the IrfanView - Adobe 8BF Filters dialog box, it will remain there until you remove it. You should not have to repeat this procedure.
Note that if in the future you choose to uninstall AstroFlat Pro, remember also to use one of the [ Remove ... ] buttons to remove the plug-in from IrfanView.
When you want to run AstroFlat Pro, navigate to the IrfanView - Adobe 8BF Filters dialog box by using the menus described earlier or press Control K on your keyboard. Select AstroFlat Pro in the list and press the [ Start Selected Filter ] button or just double-click AstroFlat Pro to run the plug-in.