[fjtorres]

Unless you are in the academic market, PDF is the single worst format to start with.

It hasn't been a significant format for commercial ebooks since last century, give or take a year. Most ebook stores list millions of titles for sale: few if any in PDF. The commercisl market left that behind decades ago.

Pretty much every publisher, corporate or indie, starts with ePub or one of the Amazon mobi/azw formats as they are perfectly readable on ereaders, phones, tables, PCs and Macs. PDF is pretty much limited to the larger screens.
If you don't want the bother of going through every ebookstore individually, there are aggregators like Direct2Digital and Smashwords who'll distribute it for you.

As pointed out by Darryl, above, your first decision is whether to go Amazon exclusive (and get *optional* access to Kindle Unlimited) or go "wide" through Kobo, Apple, Google, Nook, and maybe Overdrive. None of which do much business, if any, in PDF.

Now, if you are doing a textbook or scientific report with complex graphics and charts or you want to limit access to the academic world, then PDF might serve but for narrative text commerce ePub and Mobi, especially the latter, are mandatory.
That's where the customers are.