Yes! If you select the "Bring Your Own Book" mode when you start a new book on Leanpub, you can upload PDF, EPUB and/or MOBI files and sell them directly on Leanpub.
Here is a step-by-step walkthrough for setting up a book in our "Bring Your Own Book" writing mode:
Using this writing mode, if you already have a completed PDF, you don't need to reformat your book into Markdown and use the Leanpub workflow - you can just upload it.
(Please note that you can switch an existing Leanpub book to the "Bring Your Own Book" writing mode if you want to; you don't have to create a new book. Here is an article about how to switch writing modes.)
On the book's web page, we clearly indicate to customers which formats are available.
Of course, if you are starting a new book, we recommend that you use one of our own book writing workflows, so you can generate PDF, EPUB and MOBI ebook files directly from your manuscript with one click!