Harry is correct, alas.
Some PDFs need a lot of editing.
But you also mention mobi to text conversions: if it is merely the usual problem with hard carriage breaks at the end of every line (leading to line breaks in strange places) then inserting the text file into Word and running Stingo's macro can work really well.
You can find it here:
https://www.mobileread.com/forums/showthread.php?t=8793
Also people speak very highly of =X='s Book Creator tool:
https://www.mobileread.com/forums/showthread.php?t=28313
And on a Mac, I am told that you can use textmate.