diff --git a/candidats/migrations/0001_initial.py b/candidats/migrations/0001_initial.py
index bd3f605..0b13540 100644
--- a/candidats/migrations/0001_initial.py
+++ b/candidats/migrations/0001_initial.py
@@ -58,9 +58,9 @@ class Migration(migrations.Migration):
                 ('total_result_mark', models.PositiveSmallIntegerField(blank=True, null=True, verbose_name='Note finale')),
                 ('accepted', models.BooleanField(default=False, verbose_name='Admis')),
                 ('corporation', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='stages.Corporation', verbose_name='Employeur')),
-                ('file_resp', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='stages.Teacher', verbose_name='Exp. dossier')),
+                ('file_resp', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='+', to='stages.Teacher', verbose_name='Exp. dossier')),
                 ('instructor', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='stages.CorpContact', verbose_name='FEE/FPP')),
-                ('interview_resp', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='stages.Teacher', verbose_name='Exp. entretien')),
+                ('interview_resp', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='+', to='stages.Teacher', verbose_name='Exp. entretien')),
             ],
             options={
                 'verbose_name': 'Candidat',
diff --git a/candidats/models.py b/candidats/models.py
index 83ae97c..fcbf7ab 100644
--- a/candidats/models.py
+++ b/candidats/models.py
@@ -84,10 +84,12 @@ class Candidate(models.Model):
 
     accepted = models.BooleanField('Admis', default=False)
     interview_resp = models.ForeignKey(
-        'stages.Teacher', null=True, blank=True, related_name='+', verbose_name='Exp. entretien'
+        'stages.Teacher', null=True, blank=True, related_name='+', verbose_name='Exp. entretien',
+        on_delete=models.SET_NULL
     )
     file_resp = models.ForeignKey(
-        'stages.Teacher', null=True, blank=True, related_name='+', verbose_name='Exp. dossier'
+        'stages.Teacher', null=True, blank=True, related_name='+', verbose_name='Exp. dossier',
+        on_delete=models.SET_NULL
     )
 
     class Meta:
diff --git a/stages/pdf.py b/stages/pdf.py
index 2bca1fb..95966f1 100644
--- a/stages/pdf.py
+++ b/stages/pdf.py
@@ -34,7 +34,8 @@ class ChargeSheetPDF(SimpleDocTemplate):
 
     def produce(self, activities):
         self.story = []
-        self.story.append(Image(find('img/header.gif'), width=520, height=75))
+        header = open(find('img/header.gif'), 'rb')
+        self.story.append(Image(header, width=520, height=75))
         self.story.append(Spacer(0, 2*cm))
         destinataire = '{0}<br/>{1}'.format(self.teacher.civility, str(self.teacher))
         self.story.append(Paragraph(destinataire, style_adress))
@@ -80,6 +81,7 @@ class ChargeSheetPDF(SimpleDocTemplate):
              self.story.append(Paragraph(d, style_normal))
         self.story.append(PageBreak())
         self.build(self.story)
+        header.close()
 
 
 class UpdateDataFormPDF(SimpleDocTemplate):
@@ -100,8 +102,9 @@ class UpdateDataFormPDF(SimpleDocTemplate):
 
     def produce(self, klass):
         self.story = []
+        header = open(find('img/header.gif'), 'rb')
         for student in klass.student_set.filter(archived=False):
-            self.story.append(Image(find('img/header.gif'), width=520, height=75))
+            self.story.append(Image(header, width=520, height=75))
             self.story.append(Spacer(0, 2*cm))
             destinataire = '{0}<br/>{1}<br/>{2}'.format(student.civility, student.full_name, student.klass)
             self.story.append(Paragraph(destinataire, style_adress))
@@ -180,6 +183,7 @@ class UpdateDataFormPDF(SimpleDocTemplate):
             self.story.append(Paragraph("Pas d'élèves dans cette classe", style_normal))
 
         self.build(self.story)
+        header.close()
 
     def is_corp_required(self, klass_name):
         return any(el in klass_name for el in ['FE', 'EDS', 'EDEpe'])