PDF is a convenient format when I ask publishers if I can buy an electronic copy of whatever book I want to read, assuming it's not on any of the blind libraries I have access to. I don't however like PDF as a format for reading books .... mostly because I don't really know whether I can do things like add bookmarks for where I'm up to, but also because I find the keyboard shortcuts for next page and previous page tend to bhehave quite erratically.
Acrobat Reader DC has an option in the file menu to save as text, which works but sometimes makes a mess of the layout.
I purchased a copy of ABBYY 12 and find that my best option for converting to a plain text file. I use the new task / open PDF or image and OCR the text into Word. Because I don't enjoy reading a whole book in Word any more than I do in Acrobat, I then copy all the text in the Word doc and pop it into a plain .txt file. That way I can read as much as I like and use character combinations like zzz immediately before a chapter heading, or xxx as a marker of something else that I want to be able to easily find. Then it's just a question of using NVDA+CTRL+F, or CTRL+F in Notepad, to find the text, heading up or down,. The hanbdy part of this is that you can jump to the bottom of the text and search for whichever marker you used, and the first one you come to searching form bottom to top, is the point at which you stopped reading.
I am going to give that PDF2txt program a try, because that'd speed the conversion up a bit if it works as well as ABBYY OCRing. Obviously the benefit with ABBYY is also when, as previously mentioned, a PDF book can comprise photos of each page, or sometimes the publisher has sent it to you security protected, in which case you can't use Adobe to save the file as txt, but ABBYY will be able to convert it into Word / txt format with relatively few letter corrections needed, such as the capital letter I being misidentified as the number 1.I came across a very curious one the other day which took me an age to figure out ... ABBYY thought there was a word 'ori' and I couldn't for the life of me figure out what that was supposed to be! It turned out, with sighted assistance, to be the word 'on'!
Hope this helps :)