[Zubersoft]

If you are using the Share->Export files feature and you want to generate PDFs for each song, the settings you choose for the export are very important for determining what is generated. If you check the option to use the page order of the song, then it will generate a new PDF using only the pages needed by that song. If you select the option to "Export iOS copmatible annotations", it's going to have to generate entirely new images for every page, and the PDF library I'm using doesn't support compression, so the PDF will be many times larger than the original. It's highly recommended not to enable that setting unless you have a specific need for it.  Additionally, if you enable the option to "Draw highlights behind content", that will have to generate new images for every page of the PDF as well, because PDFs don't support a concept of putting an annotation behind the page content. So also uncheck that option unless you absolutely need it. As long as you leave those two settings off, you wil find that the PDFs that are generated during the export should be as small and fast, like the original. 

Unfortunately, I'm not sure I fully understand the question you have asked. If you are asking what happens if you select to create songs that have titles that already match ones in your library, the existing song will not be merged with the new song. It's going to create an entirely brand new song in your library. There is no option with the CSV import to update existing songs in the library at the moment.

Mike