If you don't actually know that it is not possible then don't answer peoples questions with 'it's not possible' ... it is possible and here is how ... jeepers!
Convert your books using Calibre ebook coverter (use google it's free and it's easy to use) to epub ... you can do your entire library at once .... make sure to note what folder the converted book will be going too. After you convert your files follow the following instructions;
Instructions on how to put the file in the Galaxy
1. Plug in your galaxy Tab
2. Click Mass Storage
3. Click Mount
4. On your PC (Windows 7 instructions) click on My Computer and find the Removable Disk associated with your Galaxy – For me its Removable Disk (L
5. Double Click on (L
6. Inside this drive you will see several folders .. find the one that says ‘downloads’ and double click to open that folder
7. Paste your .epub files in that folder
8. Unmount (or eject from your computer) your Galaxy Tab
9. Unplug your Tab from your computer
10. Open your readers Hub (kobo)
11. At the bottom of your Galaxy you will see the house (home page ‘button’ and to the left the rectangle thing with lines it is .. press that ‘button’
12. The menu pops up that says import content … go ahead and click that option … it even has a nice and convenient erase from other location button …
13. Wahalaaa… you can now read on your Galaxy Tablet books that were NOT bought threw Kobo … I hate companies that try to monopolize your business like that!