Fix #796

pkg/pdfcpu/annotation.go

@@ -494,14 +494,15 @@ func removeAllAnnotations(
 			return false, err
 		}
 		objNr := ir.ObjectNumber.Value()
-		if err := ctx.DeleteObject(ir); err != nil {
+		if err = ctx.FreeObject(objNr); err != nil {
 			return false, err
 		}
 		if incr {
 			// Modify Annots array obj for incremental writing.
 			ctx.Write.IncrementWithObjNr(objNr)
 		}
 	}
+
 	annots, _ := obj.(types.Array)
 
 	for _, o := range annots {
@@ -930,5 +931,12 @@ func RemoveAnnotations(ctx *model.Context, selectedPages types.IntSet, idsAndTyp
 		}
 	}
 
+	if removeAll {
+		// Hacky, actually we only want to remove struct tree elements using removed annotations
+		// but this is most probably what we want anyway.
+		root, _ := ctx.Catalog()
+		root.Delete("StructTreeRoot")
+	}
+
 	return removed, nil
 }

pkg/pdfcpu/validate/structTree.go

@@ -90,7 +90,7 @@ func validateObjectReferenceDict(xRefTable *model.XRefTable, d types.Dict) error
 	}
 
 	if obj == nil {
-		return errors.New("pdfcpu: validateObjectReferenceDict: missing required entry \"Obj\"")
+		return errors.Errorf("pdfcpu: validateObjectReferenceDict: missing obj#%s", ir.ObjectNumber)
 	}
 
 	return nil