Dr. Thomas L. Constable has authored and is providing
free a set of commentaries on the entire Bible--Old and New Testaments. They are all in the pdf format.
Frankly, I had not known of Dr. Constable before now. However, I have learned that he was a professor at Dallas Theological Seminary (a prestigious institution) until retiring in 2011. He was Senior Professor Emeritus of Bible Exposition there. There is much more about him
here.
Dr. Constable demurely says that these are "working documents" and refers to them as expository "Bible study notes" rather than commentaries. I spot-checked some of the commentaries. They are lengthy and very in-depth. They look fully developed and very professional to me. However, the ones that I saw, at least, are not formatted as books. There are no book covers, title pages, or copyright pages, for example. But if it's
content that you're interested in, I don't think that you will bothered by that.
These commentaries are expensive (at least in my way of thinking) at Amazon, being about $30 each for the least expensive copies. However, only two of the volumes are presently available for sale (Luke/John and Acts/Romans). And if you're interested in having them in a digital format, well, it looks like you are out of luck. They're only available as paperbacks at Amazon.
Follow
this link to find links to all of these
free commentaries.