PDF converter is referencing an out-dated version of pdfbox : 0.7.3. Since that version, pdfbox has moved into the apache umbrella and is now releasing the 1.5.0 version.
The 1.5.0 version of pdfbox is fixing NPE problems such as :
Caused by: org.nuxeo.ecm.core.api.WrappedException: Exception: java.lang.NullPointerException. message: null
at org.pdfbox.pdmodel.PDPageNode.getAllKids(PDPageNode.java:194)
at org.pdfbox.pdmodel.PDPageNode.getAllKids(PDPageNode.java:182)
at org.pdfbox.pdmodel.PDDocumentCatalog.getAllPages(PDDocumentCatalog.java:226)
at org.pdfbox.util.PDFTextStripper.writeText(PDFTextStripper.java:216)
at org.pdfbox.util.PDFTextStripper.getText(PDFTextStripper.java:149)
at org.nuxeo.ecm.core.convert.plugins.text.extractors.PDF2TextConverter.convert(PDF2TextConverter.java:73)
... 9 more