Many thanks for the recommendations, johnnyb, that sounds very nice. I'll take a look at
Documents first to decide if
PDF Expert is worth investing the €9. That's a relatively high price in the world of iOS, but still very low compared to "legacy" OSs like Mac OS or Windows.
PDF Expert also has suberb reviews and ratings (straight 5 stars all around, it seems) in my own micro-country's App Store, which should suggest something.
And I can see another thing PDF Expert and GoodReader have in common: both are Russian apps, and because GoodReader is commonly held to be the best PDF app on iOS, I'm sure PDF Expert did the best they could to come up with a product that could truly compete with, and exceed, GoodReader.
The same Russian developer, Readdle, offers two more apps that have outstanding reviews, Scanner Pro and Calendars, so I'll take a look at those, too. Heaven knows the default iOS Calendar app is so lame it can make you cry.
PS: All Readdle apps at a glance can be seen at
http://readdle.com/products/