What you mean with "library" ? What Windows OS or Mac OS?
Diesel eBooks that are PDF are the output of Adobe's Content Sever and have DRM applied.
To use these eBooks you need Adobe's Digital Editions.
Go to the web page http://www.adobe.com/products/digitaleditions/ for introductory information and to install.
The Adobe Digital Editions U2U Forum is at: http://forums.adobe.com/community/adobe_digital_editions
It is helpful to review the FAQ page at: http://www.adobe.com/products/digitaleditions/faq/
If you have problems installing Digital Editions this technote may help: http://kb2.adobe.com/cps/403/kb403051.html
I have Windows xp and ADE. ,book loads to read but does not go into library
so that I can transfer it to my KOBO. Only book that did load was in PDF
and it loaded upside down.
Ok. You for sure have a KOBO / ADE problem.
You'll want to look through the Digital Editions forum at http://forums.adobe.com/community/adobe_digital_editions
In particular users "Jim Lester" and "Frustrated in AZ" provide useful information.