Our friends at Readdle, the development house that makes such great apps as PDF Expert, Scanner Pro and Remarks, have an interesting proposition for iPhone users who have a Facebook account. In order to increase the number of people following Readdle on Facebook, it's willing to give away its Printer Pro for iPhone app -- usually US$4.99 -- via a Readdle Social Challenge.

Here's the challenge -- you need to help Readdle get to 10,000 "Likes" on Facebook within seven days, and then they'll give away Printer Pro for iPhone for a 24-hour period. The Social Challenge is already underway, and there's a countdown clock spinning away the days, hours and minutes until it's all over.

A little about Printer Pro might whet your appetite to hit the "Like" button; it's an iOS app to provide a simple way to print documents from your iPhone to many WiFi printers or to other printers via a free helper app for Mac or Windows.