Not sure how much was it for but it says,
◆FREE FOR A LIMITED TIME◆
It's really first app for PDF reading and annotation that doesn't overwhelm you with buttons and settings.
Keep PDFs in filing boxes to organize and find documents easier. Make it more colorful by color-coding tags. Rename or easily select and delete multiple documents. Tap the "Open In…" button to open the document in PDF Box from any other app like Mail, Safari, etc. You can also use iTunes file sharing to transfer PDFs directly from your Mac to your iPhone or iPad via USB cable or download/upload from/to iCloud Drive.
Cheers, I'd give it a go, along with my other half a dozen ones. Just wished they'd be simple to add text to forms and sign.