diff --git a/addons/account_edi_facturx/models/account_edi_format.py b/addons/account_edi_facturx/models/account_edi_format.py
index 159ec423d4b..02c0b2da64b 100644
--- a/addons/account_edi_facturx/models/account_edi_format.py
+++ b/addons/account_edi_facturx/models/account_edi_format.py
@@ -36,7 +36,7 @@ class AccountEdiFormat(models.Model):
         if not edi_document.attachment_id:
             return
 
-        pdf_writer.embed_odoo_attachment(edi_document.attachment_id)
+        pdf_writer.embed_odoo_attachment(edi_document.attachment_id, subtype='application/xml')
         if not pdf_writer.is_pdfa and str2bool(self.env['ir.config_parameter'].sudo().get_param('edi.use_pdfa', 'False')):
             try:
                 pdf_writer.convert_to_pdfa()
@@ -75,7 +75,7 @@ class AccountEdiFormat(models.Model):
         return self.env['ir.attachment'].create({
             'name': 'factur-x.xml',
             'raw': xml_content.encode(),
-            'mimetype': '/application#2Fxml'
+            'mimetype': 'application/xml'
         })
 
     def _is_facturx(self, filename, tree):
diff --git a/odoo/tools/pdf.py b/odoo/tools/pdf.py
index 3f882818cac..7da157575be 100644
--- a/odoo/tools/pdf.py
+++ b/odoo/tools/pdf.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 import io
+import re
 
 from datetime import datetime
 from hashlib import md5
@@ -18,6 +19,8 @@ from odoo.tools.misc import file_open
 
 _logger = getLogger(__name__)
 DEFAULT_PDF_DATETIME_FORMAT = "D:%Y%m%d%H%M%S+00'00'"
+REGEX_SUBTYPE_UNFORMATED = re.compile(r'^\w+/[\w-]+$')
+REGEX_SUBTYPE_FORMATED = re.compile(r'^/\w+#2F[\w-]+$')
 
 
 # make sure values are unwrapped by calling the specialized __getitem__
@@ -95,16 +98,16 @@ class OdooPdfFileReader(PdfFileReader):
 
         try:
             file_path = self.trailer["/Root"].get("/Names", {}).get("/EmbeddedFiles", {}).get("/Names")
+
+            if not file_path:
+                return []
+            for i in range(0, len(file_path), 2):
+                attachment = file_path[i+1].getObject()
+                yield (attachment["/F"], attachment["/EF"]["/F"].getObject().getData())
         except Exception:
             # malformed pdf (i.e. invalid xref page)
             return []
 
-        if not file_path:
-            return []
-        for i in range(0, len(file_path), 2):
-            attachment = file_path[i+1].getObject()
-            yield (attachment["/F"], attachment["/EF"]["/F"].getObject().getData())
-
 
 class OdooPdfFileWriter(PdfFileWriter):
 
@@ -117,21 +120,29 @@ class OdooPdfFileWriter(PdfFileWriter):
         self._reader = None
         self.is_pdfa = False
 
-    def addAttachment(self, name, data, subtype=""):
+    def addAttachment(self, name, data, subtype=None):
         """
         Add an attachment to the pdf. Supports adding multiple attachment, while respecting PDF/A rules.
         :param name: The name of the attachement
         :param data: The data of the attachement
         :param subtype: The mime-type of the attachement. This is required by PDF/A, but not essential otherwise.
-        It should take the form of "/xxx%2Fxxx". E.g. for "text/xml": "/text%2Fxml"
+        It should take the form of "/xxx#2Fxxx". E.g. for "text/xml": "/text#2Fxml"
         """
-        if subtype == 'application/xml':
-            subtype = '/application#2Fxml'
+        adapted_subtype = subtype
+        if subtype:
+            # If we receive the subtype in an 'unformated' (mimetype) format, we'll try to convert it to a pdf-valid one
+            if REGEX_SUBTYPE_UNFORMATED.match(subtype):
+                adapted_subtype = '/' + subtype.replace('/', '#2F')
+
+            if not REGEX_SUBTYPE_FORMATED.match(adapted_subtype):
+                # The subtype still does not match the correct format, so we will not add it to the document
+                _logger.warning("Attempt to add an attachment with the incorrect subtype '%s'. The subtype will be ignored.", subtype)
+                adapted_subtype = ''
 
         attachment = self._create_attachment_object({
             'filename': name,
             'content': data,
-            'subtype': subtype,
+            'subtype': adapted_subtype,
         })
         if self._root_object.get('/Names') and self._root_object['/Names'].get('/EmbeddedFiles'):
             names_array = self._root_object["/Names"]["/EmbeddedFiles"]["/Names"]
@@ -163,9 +174,9 @@ class OdooPdfFileWriter(PdfFileWriter):
                 NameObject("/AF"): attachment_array
             })
 
-    def embed_odoo_attachment(self, attachment):
+    def embed_odoo_attachment(self, attachment, subtype=None):
         assert attachment, "embed_odoo_attachment cannot be called without attachment."
-        self.addAttachment(attachment.name, attachment.raw, attachment.mimetype)
+        self.addAttachment(attachment.name, attachment.raw, subtype=subtype or attachment.mimetype)
 
     def cloneReaderDocumentRoot(self, reader):
         super().cloneReaderDocumentRoot(reader)