--- poppler-21.01.0/poppler/Form.cc
+++ poppler-21.01.0/poppler/Form.cc
@@ -603,7 +603,7 @@ bool FormWidgetSignature::signDocument(c
 // Get start and end file position of objNum in the PDF named filename.
 bool FormWidgetSignature::getObjectStartEnd(GooString *filename, int objNum, Goffset *objStart, Goffset *objEnd)
 {
-    PDFDoc newDoc(filename);
+    PDFDoc newDoc(filename->copy());
     if (!newDoc.isOk())
         return false;