There are several ways to transfer files from another app so you can convert them into a PDF.

From inside other apps
You can use the Action/Share menu inside other apps to choose the Print n Share Pro print icon. If you do not see the print icon, scroll to the bottom of the screen and tap on "More/..." to choose it.
Tap on "Choose" in the Print n Share Pro print screen and then choose the "Convert to PDF" printer to save the item as a PDF. Tap here (View) for details.

Use "Open in" from your other app and select Print n Share Pro
Print n Share Pro should open and display the print screen.
Tap "Choose" in the Print screen and then select the "Convert to PDF" option and Tap Save.

Share via iCloud/Dropbox/Box.net
If the other app supports Cloud Servers you can also use that to transfer files
In the other app save your file to your preferred cloud server
Open Print n Share Pro and go to the Cloud Server screen from the Files screen
Select your Cloud storage service or tap the + to set it up
Select the files and tap the Print button. Then tap "Choose" in the Print screen and then select the "Convert to PDF" option and tap Save.