Cannot import second set of CDA files in iTunes for WIndows 12.7
I am running iTunes 12.7 and I imported on set of files with CDA extensions and it converted the audiobook into MP4 files perfectly. When I went to import the second audiobook set of files, it does nothing. I get no error message unless there is somewhere else to go to see a message. I have been using iTunes for awhile but still a newbie in use and navigation. There is no bar to show progress or anything so you cannot even see if there is any progress. Do I have to get software to convert these files first (the files are on a USB stick as were the first set of files)? If I need some software to convert, why did the first set convert, can you recommend free software for Windows 10, and what kind of file should I convert to for this (mp4)?
Thanks in advance (do not have much knowledge in audio).