I had copied a .PNG file into the source folder and wanted to import it into the Lightroom catalog.
However the import dialog does not show that file in the source folder at all.
I also tried the method of selecting the source folder and using the "Synchronize" option. But that did not show the .PNG file either.
My clumsy work-around was to open the file in CS6 and save it as a .JPG file.
So my question: how can I tell Lightroom which file types (extensions) I want to be able to import?