The Keep/Copy function is intended to provide single-click copy of images to a preset folder and is meant to be as simple and fast a possible.
The naming behavior is controlled by preference options in the following manners:
No renaming, no overwrite: files are copied as-is but name conflicts can occur if files with the same name are already present in the destination folder, in which case the program asks for permission before overwriting the destination file(s).
No renaming, automatic overwrite: files are copied as-is and any existing file with the same name in the destination folder are automatically overwritten.
Automatic renaming: the program creates a new name on-the-fly as files are copied. The new name is composed as follow: SessionDate_SessionTime_SessionAutoIncrementNumber_OriginalFilename. This scheme creates essentially unique names and minimizes the risk of conflicts in the destination folder.
The program can also preserve the sub-folder hierarchy when copying to the destination folder. As a simple example, say the images being browsed are in C:\Images and the keep/copy folder selected is C:\Keepers. Say the C:\Images folders contains sub-folders, e.g. Sunsets, Kittens, Flowers, etc, etc. Without hierarchy preservation, C:\Images\Kittens\Misty.jpg will be copied to C:\Keepers\Misty.jpg while, whith folder hierarchy preservation enabled, the file would be copied to C:\Keepers\Kittens\Misty.jpg
All these options can be enabled independently or together from the program options (see the first 3 options in the Menu->Options->File Operations preference dialog page)
Now on to your question: the renaming behavior of the keep/copy function described above in driven by a renaming template. FastPictureViewer Professional let you edit this template to anything you like, simply press F2 with an image displayed, chose "Edit Templates" in the "renaming template" list, select the "Keep / Copy Renaming Template" in the editor and modify it to your liking.
The default template is "{AppStartDate:6}_{AppStartDate:11}_{SessionKeepCopyIndex:4}_{FileName}" but can be changed to anything else, for example it could include information extracted from the EXIF fields. There is no need to actually rename the current file. The saved template will be in effect immediately if you enable the first of the 3 options discussed above, called "prefix" in the program options as the default renaming template actually prefixes the file name with the date etc.
You can find more information about advanced renaming on the
tutorial's page.