Sejda can do a lot of things and still have a clean, intuitive interface, with virtually no learning curve. It has a desktop application, which makes all the difference to me, there is no need to use web apps. You can quickly manipulate PDFs, such as filling out forms sent in PDFs, inserting an illustration containing your physical signature of the document (not a digital signature, just an illustration representing your signature). I think of everything, what I like the most is the speed at which I can do all this with Sejda. It's not time consuming.