Yes. The first page of an EPUB rendered as a BMP makes a good document thumbnail or preview card. Every page is converted here, so take the first BMP from the set, or convert the EPUB to PDF and use the PDF to BMP converter with First page only to get a single file.
It depends on the size and length of the file. Small documents and images are usually ready quickly. Long videos take the longest, because most video conversions re-encode every frame.
