What format does an ebook file has?

What format do eBook have? I have a few books that i downloaded in PDF format, and i was thinking about converting the files from PDF to whatever format ebook has. I have a kobo eReader. When i put the PDF books in the kobo, the letters were too small. I tried zooming on it, but it was frustrating to wait till... show more What format do eBook have? I have a few books that i downloaded in PDF format, and i was thinking about converting the files from PDF to whatever format ebook has. I have a kobo eReader. When i put the PDF books in the kobo, the letters were too small. I tried zooming on it, but it was frustrating to wait till it moved from one side to the other just to read about two words (then i have to move back to read the rest of the sentence)!! I bought it yesterday and I'm really frustrated with my kobo! Any solutions?
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