Sadly, PDF Expert does not offer much that Adobe Acrobat won't already give you. I've spent a considerable amount of time checking out the PDF alternatives for the Mac, and most of them don't offer much value beyond that of Adobe's offering. The only difference is that most of the other offerings are less expensive albeit with less features, or an incomplete feature set. Some of the alternatives can be purchased outright rather than as a subscription like Adobe Acrobat. For most users who just want to view and do a few very basic things with PDFs, either Preview, Adobe Acrobat Reader or Foxit PDFReader are fine choices.
You're right in that people can often do what they want with Preview, Reader etc, and PDF Expert gives you nothing that Acrobat can't give you, but as mentioned up there somewhere ^^, the only thing I can find that Acrobat gives you is sharing and creating forms. If that isn't what you need then PDF Expert at 1/3 the cost of Acrobat is a strong choice.
No, it's not right for people to pirate software, but Adobe, like many companies, has created a business market monopoly on its products. And they charge accordingly. If they can be as greedy as they are, then you will get people on the other side of the scales doing the exact same thing.
I used to think that way about PDF Expert, until I actually tried using it as a daily replacement for Acrobat in my work. Many of the features are indeed there, but are often buggy, incomplete or do not work as well as Acrobat. The same goes for most other PDF software developers. Many of the bilingual PDFs I have to handle on a daily basis fail to display correctly in PDF Expert, and the app wasn't as stable as I'd hoped it would be. I may go back and revisit that app someday to see how it's evolved, but I wasn't particularly impressed by my findings last year.
The fact is, Adobe has always had the cornerstone on PDFs, for better or for worse. (Maybe "monopoly" would be a more realistic term for this...) Adobe opened up their patent on PDFs in 2008, but I really don't feel that the market has made a reader/editor that surpasses Acrobat in terms of stability and functionality. After all, Adobe developed the PDF format, nearly three decades ago.
I grew up on Windows and switched to Mac back in 2006. I continue having to use Windows for work. Back then it blew my mind that on a mac you could "just open a PDF just like that" when on Windows back then you still needed at least Acrobat Reader (even while free, you needed to make the effort to download and install it). Simply saving a document to PDF? Back then, unheard of. To this day, so many functions come native on a Mac that still aren't easily implemented in Windows.
I hate that everything has switched to subscription with a passion, particularly Adobe. I'm a Prosumer, I'm more than happy to pay my share to the software developers every few years, but I'm simply not in the position of needing the latest and newest software updates the second they're available. As such, particularly with Adobe I've been forced to pay massive premiums to before because of that (before I would get the edu suite for maybe $300ish and use it for 4-5 years' now I'm paying that in a single year even with edu discount).
I get Adobe Acrobat bundled in my Adobe subscription. I'm not sure I would pay *just* for Acrobat. What I have found in all these years is that I very very very rarely actually end up opening a PDF in Acrobat; 98% of the time Preview is more than sufficient. However, if you're someone who relies on the more advanced functions on a daily basis, they're probably in a position to be able to afford the Acrobat subscription.
In my experience over all these years, leading software has been leading software for a reason. Monopolies are always a problem, especially when we're talking about software that costs thousands for a single license. I have to use a number of those: Adobe, Esri, Matlab, ... I wouldn't be able to use them if I didn't get edu discounts. But all the opensource and/or cheaper alternatives I've tried ended up subpar at best and buggy, usually. And that's a comfort level I'm not willing to give up and am willing to pay a premium for. (another example had been Gimp vs. Photoshop; qGIS vs ArcGIS though admittedly I've been told qGIS has gotten better; I'm a hardcore R user and R definitely has been one of the better open source success stories, nevertheless I sometimes have to go back to Matlab for some functionality)
As with this example of PDF Expert, it's not exactly cheap software. Is it cheaper than the Adobe subscription? Yes. But when you actually look at it, if you really do need the functionality beyond what Preview can give you, you're probably better of just paying for "the real thing".
I've seen this over the years, often these bundles have software no mac user really needs. But they make you feel like you're getting a great deal while particularly feeding into the mindsets of those coming from Windows that you actually need all those - when in reality, most probably you don't - because that's just how it was and is on Windows. It's quite a great marketing scheme, actually.