Convert PDF to text-only file for better reading on tablet or smartphone

Aside from the great guidance you've received from George, Gary and JR_Boulay, what exactly are you using to perform PDF editing in that document?

If you have an active (paid) subscription of Adobe Acrobat Pro DC (full dektop version), you should be able to also employ the "Edit Text & Images" tool.

If you're a MS Windows or a Micrososft Office user, for example, and you are used to editing text documents with MS Word, you'll notice that the same may not be true when you're using a PDF editor (such as Acrobat);  some text and images editing limitations do exist, but there are other approaches that may be useful.

However, even when Adobe Acrobat will pose some limitations, I don't see why you can't use the "Edit Text & Images" tool to copy all the desired text into a new text box, remove all the undesired columns of  text (in which case when you employ the "Edit Text & Images" tool they should appear as editable text boxes). With that said,  you may also choose a different Font type and increase/decrease the Font size as desired for those text boxes.

You should try the Autotag tool, it can't do miracles but it should detect at least the text columns :

When performing your Save as…, select "Text (Plain)" and that will do about as good a job as possible from Acrobat. This will also strip all formatting from the document which may or may not be a good thing for you. (It has been for me, FWIW.)

However, if your original copy has things like sidebars and other copy inside the text, it's almost impossible for Acrobat to know which line of text to follow and which is separate blocks of text. As such you might have to do some post-operation cutting and pasting to put things in an order that provides the best structure for YOU.

Here's an example where it moved all of the columns of text into one spread but put the sidebar in a linear fashion.

For Android/iOS you can try liquid mode. 

For win/osx try zoom-reflow (Ctrl+4 / CMD+4 shortcuts).