I suspect it's a library conflict. Do you have fontbox-1.8.5.jar, joda-time-1.6.2.jar and pdfbox-1.8.5.jar in the userlib folder of your project?
You should remove these (see release notes of the module for more details).
Open the project in eclipse.
Go to the error and use quick fix from the context menu, this will give you the option to add the throws declaration to fix the error.
Strange, I thought this error had already been corrected. Are you sure you have downloaded the latest version from the App Store?
If you still have the error, you could try the following. Edit ...\javasource\communitycommons\Misc.java
Add the line in the import section (about line 24) : import org.apache.pdfbox.exceptions.COSVisitorException;
Edit the line (about line 641) to add the COSVisitorException, like
public static boolean overlayPdf(IContext context, IMendixObject generatedDocumentMendixObject, IMendixObject overlayMendixObject) throws IOException, COSVisitorException {
Hope this helps.