- with the crop function in Goodreader remove as much as possible margin left & right. This might cut text in the header/footer eg the page number. Optionally crop odd & even pages differently.

- turn the iPad landscape and with 2 fingers pinch to zoom the text until the margins snap to the sides of the screen. Now with a single finger scroll down to read the text from top to bottom. Flip to the next page by swiping with a single finger to the left and Goodreader will conveiniently start at the top of the next page.

In my experience for most portrait pages this enlarges the text big enough. As a bonus you can use the iPad Smart Cover as a stand in either position. I use this trick since the original iPad1 as Goodreader has been there since day 1.