Okay so I can't give you PDFs for most of these cause that would be illegal I'm pretty sure. What I can do is give you a good selection of the titles in my personal library that are useful for starting out in understanding trade in the ancient world. Most of these are focused around Roman trade because points at flair, but I'll try to include some others as I can. With most of these, I highly recommend your local/university research library. Thorough academia does not make itself particularly accessible, but librarians are heckin' awesome and have made it their life goal to help you with this knowledge. Use them, hug them, and bring them cookies. They deserve all of the above, and giving them the opportunity to help you will often make their day.

• The Roman Empire and the Indian Ocean, by Raoul McLaughlin.

This one's quite solid, quite accessible, and is a great introduction to Roman trade in the Indian ocean, as per the title. It's well written and well-cited, which gives an educated non-specialist a great introductory view into the topic. The book itself is short and won't give you everything that a more specialized book would, but it's certainly a great start.

• Rome and the Distant East: Trade Routes to the Ancient Lands of Arabia, India, and China, by Raoul McLaughlin.

Written by the same authour, it's a bit more in-depth and offers more information about land trade routes between Rome and the East. It'll give you the previous book, but better. Unfortunately, it's not particularly accessible, with the version on Amazon coming out to....about $150. Which is a painful penny. Use your local library on this one, because while it's got some frankly amazing stuff, such as this handy dandy chart, you shouldn't have to pay $150 to see the things within.

• Trade, Commerce, and the State in the Roman World, eds. Andrew Wilson and Alan Bowman.

This is another seminal work on the topic, and it's one that I use extensively. It goes through everything you could ask for and some things that you haven't even thought about, including stuff on textiles, stone, glass, pottery, and wood, all of which were integral parts of the Roman world. Again, inaccessible, use your library.

• Early Exchange between Africa and the Wider Indian Ocean World, ed. Graham Campbell, especially ch. 5, "Early Greek and Latin Sources on the Indian Ocean and Eastern Africa"

I can actually hyperlink to this one because the professor who wrote said chapter is a pretty amazing person and has included the chapter on his Academia. The book as a whole is pretty spectacular, and the reason I specify that chapter (besides the fact that free is good) is because it gives you a great introduction to the primary sources for the region, including the famed Periplus of the Erythrian Sea and the Muziris Papyrus.

• The Cambridge Companion to the Roman Economy, ed. Walter Scheidel.

Cambridge Companions are good, and Scheidel is one of the best scholars in the field. This one is more focused on the Roman world, but gives a great overview of both modern studies in the field and more specialized aspects thereof. Each chapter is written by an exemplary scholar, and each of them is thoroughly sourced and quite readable. The Cambridge Companions are also (quelle horreur) reasonably accessible-ish, with prices being somewhere around $30-40, if you'd prefer to buy them, and are generally accessible to libraries.

• The Cambridge Economic History of the Greco-Roman World, eds. Walter Scheidel, Ian Morris, Richard Saller.

Same idea as above, just with a wider scope.

• The Romans and Trade by Andre Dchernia (there's an English translation that's quite good)

Sadly inaccessible (not even showing up on Amazon whatsoever), but the title says it all. This book gives a ridiculously thorough breakdown of Roman trade that considers trade both within and outside of the Empire. Food supplies and logistics of said trade get some healthy coverage, as well as legal things that affected trade, methods and means of transport, etc. Quite good, if you can get your hands on it.

• The Customs Law of Asia

It's another fantastic (and inaccessible :( ) book that's been put out on customs laws and prices about trade. The central focus of the book is an inscription that's been found with...well....customs law. If you're interested in Roman customs and enforcement, this is a superb place to start.

• Rome and the Indian Ocean Trade from Augustus to the Early Third Century CE by Matthew Adam Cobb

Yet another $150 book, use your library. The title really explains it all, though the book totally cheats a little and has a section on pre-Augustan Indian trade. The book covers trade going both ways, to India and to Rome, looks into archaeological finds, discusses the organization, state support, trade routes, trade (im?)balance, and development over the centuries.

Again, this is just a small sample of books, but I really do hope that it helps. I tried to include a couple that you can find without too much headache/expense, and if you need me to see what I can do about finding any others I'll be happy to scout around (or just find journal articles, cause those are usually a little bit easier to find, such as the very well written "Caravan cities: the Roman Near East and long-distance trade by land"). The topic is unfortunately rather insular (for some reason, academics are pretty certain that no one wants to know about it, which I find preposterous), but I'm always happy to chat about it.