Indexing unprintable/encrypted PDFs fails

While reindexing, the pdf extractor can report this error:

java.lang.NoClassDefFoundError: org/bouncycastle/jce/provider/BouncyCastleProvider

at org.pdfbox.pdmodel.PDDocument.openProtection(PDDocument.java:905)

at org.pdfbox.pdmodel.PDDocument.decrypt(PDDocument.java:489)

at com.atlassian.bonnie.search.extractor.PdfContentExtractor.extractText(PdfContentExtractor.java:46)

at com.atlassian.bonnie.search.extractor.BaseAttachmentContentExtractor.addFields(BaseAttachmentContentExtractor.java:31)

at com.atlassian.bonnie.search.BaseDocumentBuilder.getDocument(BaseDocumentBuilder.java:28)

at com.atlassian.confluence.search.lucene.ConfluenceObjectToDocumentConverter.convert(ConfluenceObjectToDocumentConverter.java:20)

at com.atlassian.confluence.search.lucene.ConfluenceObjectQueue$1.indexCollection(ConfluenceObjectQueue.java:75)

at com.atlassian.bonnie.index.QueueProcessingRunnableImpl.run(QueueProcessingRunnableImpl.java:39)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

at java.lang.reflect.Method.invoke(Method.java:585)

at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:284)

at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:155)

at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:122)

at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:56)

at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:144)

at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:174)

at $Proxy62.run(Unknown Source)

at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:987)

at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:528)

at java.lang.Thread.run(Thread.java:595)