I have a number of free ebooks and pdfs maintained under Adobe Digital Edition. I would like to move all of them to Calibre which I use to maintain my ebooks library on another PC. The Calibre tool is also used by me to manage my Kindle PaperWhite. How do I do that ?
The simple, answer is that you export the PDFs to files on your disc and then use the add books function of Calibre to add them (or drag and drop) to get them into Calibre.
Any files that have DRM you will not be able to import and read, but you should continue to use these on ADE. Removing the DRM is probably against the law.
Once you have the files adding the ebooks that have correct metadata should give you little problems. Calibre will ignore a lot of the PDF metadata during addition, I am not sure if it just tries to extract the title from the filename, but up to 2.19 my Calibre (on Linux Mint 17.1) would not extract the author from the appropriate metadata field. I always add PDF files using a python script that extracts the Title and Author from the PDFs metadata and then calls
calibredb add -t Title -a Author.
I used that to add other files to Calibre as well because the script does some basic clean up, e.g. on the author's name (changing "Lastname, Firstname" into correct "Firstname Lastname" form etc).
You can of course also add your ebooks using
calibredb add that way too.