I have been using Calibre for several years but I am certainly no expert.
Some background on my process in my introduction to Calibre,
"My Calibre Usage..."
As I said in the introduction, I used Calibre to produce readable PDFs from eBooks formats but in the past they could not be searched, so I would then GhostScript to coimplete the conversion process.
In Calibre version 5.4.2 the search problem vanished, producing a readable and searchable PDF in a single pass without the second step of GhostScript.
Sample: First Principles - Thomas E. Ricks 01.pdf
I was thrilled, but when I upgraded to the next version of Calibre 5.6.0 a new problem became evident despite using the same settings.
Hard to describe, better to show the sample than try to describe but the the text is horizontally compressed.
Sample: First Principles - Thomas E. Ricks 01.pdf
I had to back down to the previous version but this will not lat forever as I will need to upgrade at some point.
I also included the epub sample: First Principles - Thomas E. Ricks.epub
Thank you.