Conversion might fail because of any of the following reasons:
Some PDF files may have too many images - maybe the pages themselves are images, or there might be a large background image, or sometimes, each page has text superimposed on a corresponding image. In such cases, the conversion will fail.
If the PDF file has too many images, and server is facing many conversions at the same time, your conversion might take too long, and hence fail. In such cases, try again after a few hours.
These are some indicators of your PDF file having too many images
SmoothPDF Converter can send the converted eBook to your verify email address. Sign in with your email address, and check the corresponding box when starting a new conversion.
You can email the converted book to your Kindle device, or Kindle app on your phone. Just follow the instructions on Send to Kindle By Email page
You can install a mobi reader from the Google Play Store to read mobi format ebooks on your phone. Search for a mobi reader
You can also read mobi format ebooks on the Kindle app on your phone. Just email the ebook to your Kindle app as an attachment, as mentioned in #1 above.
You can install a ePub reader from the Google Play Store to read epub format ebooks on your phone. Search for an ePub reader