Extern in .cpp files is a code smell.

fpdfsdk/src/fsdk_mgr.cpp

Index: fpdfsdk/src/fsdk_mgr.cpp
diff --git a/fpdfsdk/src/fsdk_mgr.cpp b/fpdfsdk/src/fsdk_mgr.cpp
index 67dea80d0dd17b49d64ad16f439e36fe74fe098b..fa270cc2892a2eeecbf2a56e645903deba253c46 100644
--- a/fpdfsdk/src/fsdk_mgr.cpp
+++ b/fpdfsdk/src/fsdk_mgr.cpp
@@ -916,16 +916,9 @@ FX_BOOL CPDFSDK_PageView::OnKeyDown(int nKeyCode, int nFlag) {
 }
 
 FX_BOOL CPDFSDK_PageView::OnKeyUp(int nKeyCode, int nFlag) {
-  //  if(CPDFSDK_Annot* pAnnot = GetFocusAnnot())
-  //  {
-  //      CFFL_IFormFiller* pIFormFiller = g_pFormFillApp->GetIFormFiller();
-  //      return pIFormFiller->OnKeyUp(pAnnot, nKeyCode, nFlag);
-  //  }
   return FALSE;
 }
 
-extern void CheckUnSupportAnnot(CPDF_Document* pDoc, CPDF_Annot* pPDFAnnot);
-
 void CPDFSDK_PageView::LoadFXAnnots() {
   CPDFDoc_Environment* pEnv = m_pSDKDoc->GetEnv();