diff --git a/CHANGES.rst b/CHANGES.rst
index 1e1cc21..8532d0e 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -6,6 +6,8 @@ Changelog
 
 - Do not let `Recreate session` when it is `sent` or `signed`.
   [gbastien]
+- Formalised the sent filename generation in `ISignable.get_filename` (PARAF-550).
+  [chris-adam]
 
 1.0.2 (2026-08-24)
 ------------------
diff --git a/src/imio/esign/adapters.py b/src/imio/esign/adapters.py
index 5cc9646..08bd080 100644
--- a/src/imio/esign/adapters.py
+++ b/src/imio/esign/adapters.py
@@ -2,6 +2,8 @@
 
 from imio.esign.utils import get_session_annotation
 from imio.esign.utils import get_session_info
+from imio.helpers.transmogrifier import get_correct_id
+from os import path
 from plone.memoize import ram
 from zope.interface import Interface
 
@@ -80,6 +82,10 @@ def get_discriminators(self):
     def get_create_session_custom_data(self):
         return {}
 
+    def get_filename(self, annex, existing_files=()):
+        filename, ext = path.splitext(annex.file.filename or u"no_filename.pdf")
+        return get_correct_id(existing_files, filename) + ext
+
 
 class ISignable(Interface):
     def get_signers(self):
@@ -118,3 +124,12 @@ def get_create_session_custom_data(self):
         in the annotation.
         """
         return {}
+
+    def get_filename(self, annex, existing_files=()):
+        """
+        Return the filename to use for that element in the session.
+
+        `existing_files` holds the names (without extension) already used in the
+        session, to keep them unique.
+        """
+        return u""
diff --git a/src/imio/esign/configure.zcml b/src/imio/esign/configure.zcml
index de4a599..761425e 100644
--- a/src/imio/esign/configure.zcml
+++ b/src/imio/esign/configure.zcml
@@ -18,6 +18,11 @@
   <include package=".browser" />
   <include package=".services" />
 
+  <adapter
+    factory=".adapters.SignableAdapter"
+    provides=".adapters.ISignable"
+    for="*" />
+
   <adapter
     factory=".adapters.DefaultContextUidProvider"
     provides=".interfaces.IContextUidProvider"
diff --git a/src/imio/esign/events.py b/src/imio/esign/events.py
index 2afa7f2..63a2f03 100644
--- a/src/imio/esign/events.py
+++ b/src/imio/esign/events.py
@@ -1,10 +1,11 @@
 # -*- coding: utf-8 -*-
 
+from Acquisition import aq_parent
+from imio.esign.adapters import ISignable
 from imio.esign.utils import get_file_info
 from imio.esign.utils import get_session_annotation
 from imio.esign.utils import get_sessions_for
 from imio.esign.utils import remove_files_from_session
-from imio.helpers.transmogrifier import get_correct_id
 from os import path
 
 
@@ -57,10 +58,12 @@ def on_categorized_annex_updated(annex, event):
                     file_data["scan_id"] = annex.scan_id
                     # filename changed, need to make sure new filename is unique
                     if annex.file.filename != file_data["filename"]:
-                        existing_files = [path.splitext(f["filename"])[0] for f in session["files"]]
-                        filename, ext = path.splitext(annex.file.filename)
-                        new_filename = get_correct_id(existing_files, filename)
-                        file_data["filename"] = new_filename + ext
+                        existing_files = [
+                            path.splitext(f["filename"])[0] for f in session["files"] if f["uid"] != annex_uid
+                        ]
+                        file_data["filename"] = ISignable(aq_parent(annex)).get_filename(
+                            annex, existing_files=existing_files
+                        )
                     # file_uid is only there one time per session
                     break
 
diff --git a/src/imio/esign/testing.zcml b/src/imio/esign/testing.zcml
index a3aa086..c65a9bc 100644
--- a/src/imio/esign/testing.zcml
+++ b/src/imio/esign/testing.zcml
@@ -7,9 +7,4 @@
 
   <include file="configure.zcml" />
 
-  <adapter
-      for="*"
-      factory="imio.esign.adapters.SignableAdapter"
-      provides="imio.esign.adapters.ISignable"/>
-
 </configure>
diff --git a/src/imio/esign/tests/test_adapters.py b/src/imio/esign/tests/test_adapters.py
index b84ac6a..e9328e5 100644
--- a/src/imio/esign/tests/test_adapters.py
+++ b/src/imio/esign/tests/test_adapters.py
@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 
 from imio.esign.adapters import DefaultContextUidProvider
+from imio.esign.adapters import ISignable
+from imio.esign.adapters import SignableAdapter
 from imio.esign.interfaces import IContextUidProvider
 from imio.esign.interfaces import IItemOrderProvider
 from imio.esign.tests.base import BaseEsignTest
@@ -35,3 +37,25 @@ def test_get_item_order(self):
         empty = api.content.create(container=self.portal, type="Folder", id="empty-folder")
         provider = getAdapter(empty, IItemOrderProvider)
         self.assertEqual(provider.get_item_order(), {})
+
+
+class TestSignableAdapter(BaseEsignTest):
+
+    def test_get_filename(self):
+        annex = self.portal["folder0"]["annex0"]
+        adapter = getAdapter(annex.aq_parent, ISignable)
+        self.assertIsInstance(adapter, SignableAdapter)
+        self.assertEqual(adapter.get_filename(annex), u"annex0.pdf")
+        # a name already used in the session gets a numbered suffix
+        self.assertEqual(adapter.get_filename(annex, existing_files=["annex0"]), u"annex0-1.pdf")
+        self.assertEqual(adapter.get_filename(annex, existing_files=["annex0", "annex0-1"]), u"annex0-2.pdf")
+        # a __<uid> suffix is kept: imio.zamqp parses it back
+        annex.file.filename = u"Rapport__{}.pdf".format(annex.UID())
+        self.assertEqual(adapter.get_filename(annex), u"Rapport__{}.pdf".format(annex.UID()))
+        # and it survives deduplication, the suffix landing after the uid
+        self.assertEqual(
+            adapter.get_filename(annex, existing_files=["Rapport__{}".format(annex.UID())]),
+            u"Rapport__{}-1.pdf".format(annex.UID()),
+        )
+        annex.file.filename = None
+        self.assertEqual(adapter.get_filename(annex), u"no_filename.pdf")
diff --git a/src/imio/esign/tests/test_events.py b/src/imio/esign/tests/test_events.py
new file mode 100644
index 0000000..da1699e
--- /dev/null
+++ b/src/imio/esign/tests/test_events.py
@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+"""events tests for this package."""
+from imio.esign.tests.base import BaseEsignTest
+from imio.esign.utils import add_files_to_session
+from zope.event import notify
+from zope.lifecycleevent import ObjectModifiedEvent
+
+
+class TestEvents(BaseEsignTest):
+    def test_on_categorized_annex_updated(self):
+        """Renaming an annex keeps its session filename unique, without conflicting with itself."""
+        signers = [("user1", "user1@sign.com", "User 1", "Position 1")]
+        annex0 = self.portal["folder0"]["annex0"]
+        annex2 = self.portal["folder0"]["annex2"]
+        sid, session = add_files_to_session(signers, (annex0.UID(), annex2.UID()))[-1]
+        self.assertEqual([f["filename"] for f in session["files"]], [u"annex0.pdf", u"annex2.pdf"])
+        # renamed to a name already used in the session: deduplicated
+        annex2.file.filename = u"annex0.pdf"
+        notify(ObjectModifiedEvent(annex2))
+        self.assertEqual([f["filename"] for f in session["files"]], [u"annex0.pdf", u"annex0-1.pdf"])
+        # updated again: the generated name is the one it already has, it must not drift to annex0-2.pdf
+        annex2.setTitle("New Annex 2")
+        notify(ObjectModifiedEvent(annex2))
+        self.assertEqual([f["filename"] for f in session["files"]], [u"annex0.pdf", u"annex0-1.pdf"])
+        self.assertEqual(session["files"][1]["title"], "New Annex 2")
diff --git a/src/imio/esign/utils.py b/src/imio/esign/utils.py
index ea1baa4..e107f16 100644
--- a/src/imio/esign/utils.py
+++ b/src/imio/esign/utils.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+from Acquisition import aq_parent
 from collections import OrderedDict
 from copy import deepcopy
 from datetime import datetime
@@ -19,7 +20,6 @@
 from imio.esign.interfaces import IContextUidProvider
 from imio.esign.interfaces import IItemOrderProvider
 from imio.helpers.content import uuidToObject
-from imio.helpers.transmogrifier import get_correct_id
 from imio.helpers.ws import get_auth_token
 # from imio.pyutils.system import post_request
 from imio.pyutils.utils import shortuid_encode_id
@@ -101,6 +101,7 @@ def add_files_to_session(  # noqa C901
             session = annot["sessions"][session_id]
     dispatch = session_id is None
     sessions_used = []
+    from imio.esign.adapters import ISignable  # avoid circular import
 
     for uid in files_uids:
         file_size = get_filesize(uid)
@@ -135,13 +136,11 @@ def add_files_to_session(  # noqa C901
             logger.info("File with UID %s is already in session_id %s and data were updated!", uid, session_id)
             remove_files_from_session([uid], remove_empty_session=False)
 
-        existing_files = [path.splitext(f["filename"])[0] for f in session["files"]]
-        filename, ext = path.splitext(annex.file.filename or "no_filename.pdf")
-        new_filename = get_correct_id(existing_files, filename)
+        existing_files = [path.splitext(f["filename"])[0] for f in session["files"] if f["uid"] != uid]
         file_dict = PersistentMapping(
             {
                 "scan_id": annex.scan_id,
-                "filename": new_filename + ext,
+                "filename": ISignable(aq_parent(annex)).get_filename(annex, existing_files=existing_files),
                 "title": annex.title or "no_title",
                 "uid": uid,
                 "context_uid": context_uid,