[eurasiarc]

Special thanks to DoctorOhh, Chaley and Becky for the elaborations here.

Here a few things I discovered.

First the AZW3 files are problematic if they have DRM. What I did was add a number of files of various types that I had put in a folder for processing by Calibre. These included some pdf files, a lot of epub files and a few My Kindle files that were mostly free books. It turns out that a few books that had been paid for and contained DRM protection got into the batch and these were the ones that couldn't be viewed after being sent to my Nook HD+ device, so I just deleted them and sent only files in formats that my readers, Moon+ and Adliko Pro can read. They seem to be able to read any mobi files but not azw files. Some Kindle Books, even some purchased ones don't have the DRM thing and get added to Calibre as mobi files.

As was pointed out, when you change a book from one format to another the pagination will be affected by the font and layout settings of the original so if you turn a mobi to epub or vice versa the pagination will be different. If you're trying to use some of these books as sources for a paper you might have to look at a print or pdf copy of the book to get page numbers.

Next, I was having a problem getting this stuff sent to my microSD card, because the highly irritating Nook software doesn't make it easy to move files from the built in memory card to the microSD. The Barnes and Noble tech support staff I spoke with didn't even know that the microSD card is accessible through the latest Android OS used on Nook devices. They told me that the only way I could get any files onto the microSD card was by connecting the device by usb cable to a PC (or MAC). They said that it would be impossible to access any files transferred to the microSD card from the Nook device itself and didn't even know how to identify the directory or folder name for the microSD.

I soon found that they didn't know what they were talking about. First I got an app called X-plore file manager. As soon as that was installed, I could easily see where the microSD card was located in the file system. It would have been very easy to copy files stored on the internal card onto the microSD. I also found that both Moon+ and Adliko reader can import book files that are stored in folders on the microSD once you know what folder they are in. They are in the folder /mnt/ext_sdcard.

All you have to do is look for sub folders of the /mmt folder which is in the root directory. Unfortunately neither first nor second level Nook support could tell me this.

The other thing to know is that because the Nook still uses its own cumbersome desktop, you can't see how files and folders are stored unless you install Google Play or non Barnes and Noble apps like Moon + or a file manager to see the folder and file structure.

As it turned out as soon as I plugged the Nook device into the USB port on my PC, Calbre was able to recognize the device and began allowing me to send files directly to the microSD card. Only after the device was connected by USB to the PC was Calibre able to recognize both the "Nook Drive" on the PC and the microSD drive on the device. That's the way I was able to get my Calibre library books onto the microSD card. I also could have copied or moved files from the device's internal card to the external microSD card, If I had used the file manager I obtained through Google Play Apps.

I still haven't figured out how to get Calibre Companion to find the external microSD card, but I will work at that.

Upshot. Moon and Adliko plus and pro readers appear to read mobi files but not AZW3 files.

Thanks for helping me figure these things out.