It is possible to learn how to do this. However, you should realize that graphic design is a design field you need to know quite much more than, PDF template with different styles to begin with.
First you need to know are these PDF files meant for printing. If they are you should spend a few weeks- a few months next to a printer so that you understand how the printer really works. In the beginning you can just work with a office printer if you got a very good one. You should also make a few test runs on a real commercial printer too so you know whats going to happen when you DO print final runs and you ultimately understand their process and colorspace. Pay attention to how the color reproduces on these systems, pay especially attention to how black, and very bright colors behave. Most likely you realize that you either need a Pantone color book or a hardware calibrator for your monitor, or you might expect print jobs to have surprises you didnt intend (good, or bad). Or you can just decide that this isnt important.
Second you need to pin down which software you are going to use. Also how your going to use them. The classical choice would be a InDesign, Illustrator combo. But you must be aware that the graphs in the templates you see are most likely drawn by hand, or at least substantially modified so that its almost like drawing by hand. Its surprising but thats what graphic designers tend to do, their software can not generally make cool graphs otherwise. So even when you have a template generally the graphs need to be redrawn every time you release a report. Same applies to Scribus. Adobe also has a very strict licensing rule set that does not allow you to use InDesign unattended by a human. If you need these templates for automated generation then the you need to buy InDesign server, in which case you are better of having somebody who can use it as the license is rather expensive (you could hire A graphic designer for that kind of money, most likely you would need also a in house programmer). Also consider, LATEX, Mathematica etc.
Next is making it look nice. Well I can not help with that i'm not a graphic designer my work is sort of hit and miss. Yes even after 15 years of doing stuff like this for a hobby. Its technically not all that hard, just try to set yourself a simple rule set and follow it so that your style stays consistent. It does not always work out the way I intended and I need to reiterate way too many times compared to real professionals (mainly because I don't do it as much as they do). There is no rule, you can find workable design nearly anywhere even by breaking known rules.
