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


Use "Open in" or the Share button from your other app and select Save2PDF
Save2PDF should open and display the PDF screen.
Then you can just tap on the Save button.
If you do not see the Save2PDF PDF icon, scroll to the bottom of the screen and tap on "More/..." to choose it. This is different from the colored app icons at the top.


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 Save2PDF 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 PDF button