diff --git a/backend/app/api/admin.py b/backend/app/api/admin.py
index a28d508..17d0e02 100644
--- a/backend/app/api/admin.py
+++ b/backend/app/api/admin.py
@@ -1,5 +1,6 @@
 """Admin-only API endpoints: user CRUD, invitation management, audit log."""
 
+import logging
 import secrets
 from datetime import datetime, timedelta, timezone
 from typing import Optional
@@ -17,13 +18,77 @@ from app.schemas.disclosure import (
     DisclosureCountResponse, DisclosureRequestResponse, DisclosureRequestUpdate,
 )
 from app.schemas.user import UserCreate, UserResponse, UserUpdate
+from app.config import get_settings
 from app.services.audit_service import log_action
 from app.services.disclosure_service import (
     admin_delete_disclosure, get_pending_count, reactivate_disclosure,
     review_disclosure_request, revoke_disclosure,
 )
+from app.services.notification_service import send_email
+from app.services.pdf_guide import generate_guide_pdf
 
 router = APIRouter()
+logger = logging.getLogger(__name__)
+
+_settings = get_settings()
+
+
+# ---------------------------------------------------------------------------
+# Invitation email helper
+# ---------------------------------------------------------------------------
+
+def _send_invitation_email(
+    email: str, token: str, expires_at: datetime
+) -> None:
+    """Send an invitation email with a PDF onboarding guide attached."""
+    try:
+        invite_url = f"{_settings.FRONTEND_BASE_URL}/register?token={token}"
+        pdf_bytes = generate_guide_pdf(invite_url)
+
+        expires_str = expires_at.strftime("%d.%m.%Y")
+
+        plain_body = (
+            "Guten Tag,\n\n"
+            "Sie wurden zum DAK Zweitmeinungs-Portal eingeladen.\n\n"
+            "Bitte registrieren Sie sich unter folgendem Link:\n"
+            f"{invite_url}\n\n"
+            f"Der Link ist gueltig bis zum {expires_str}.\n\n"
+            "Im Anhang finden Sie eine Anleitung (PDF) mit allen "
+            "wichtigen Informationen zur Registrierung und Nutzung "
+            "des Portals.\n\n"
+            "Mit freundlichen Gruessen\n"
+            "Complex Care Solutions GmbH"
+        )
+
+        html_body = (
+            "<div style='font-family: Arial, sans-serif; max-width: 600px;'>"
+            "<h2 style='color: #005293;'>DAK Zweitmeinungs-Portal</h2>"
+            "<p>Guten Tag,</p>"
+            "<p>Sie wurden zum <strong>DAK Zweitmeinungs-Portal</strong> eingeladen.</p>"
+            "<p>Bitte registrieren Sie sich unter folgendem Link:</p>"
+            f"<p><a href='{invite_url}' style='color: #005293; "
+            f"font-weight: bold;'>{invite_url}</a></p>"
+            f"<p>Der Link ist g&uuml;ltig bis zum <strong>{expires_str}</strong>.</p>"
+            "<p>Im Anhang finden Sie eine <strong>Anleitung (PDF)</strong> mit allen "
+            "wichtigen Informationen zur Registrierung und Nutzung des Portals.</p>"
+            "<hr style='border: none; border-top: 1px solid #dee2e6; margin: 20px 0;'>"
+            "<p style='color: #6c757d; font-size: 12px;'>"
+            "Complex Care Solutions GmbH<br>"
+            "https://dak.complexcaresolutions.de</p>"
+            "</div>"
+        )
+
+        send_email(
+            to=email,
+            subject="[DAK Portal] Ihre Einladung zum Zweitmeinungs-Portal",
+            body=plain_body,
+            html_body=html_body,
+            attachments=[
+                ("DAK-Portal-Anleitung.pdf", pdf_bytes, "application/pdf")
+            ],
+        )
+    except Exception:
+        logger.exception("Failed to send invitation email to %s", email)
 
 
 # ---------------------------------------------------------------------------
@@ -250,6 +315,10 @@ def create_invitation(
         user_agent=request.headers.get("user-agent"),
     )
 
+    # Send invitation email with PDF guide (fire-and-forget)
+    if payload.email:
+        _send_invitation_email(payload.email, token, expires_at)
+
     return invitation
 
 
diff --git a/backend/app/assets/LiberationSans-Bold.ttf b/backend/app/assets/LiberationSans-Bold.ttf
new file mode 100644
index 0000000..31ddaef
Binary files /dev/null and b/backend/app/assets/LiberationSans-Bold.ttf differ
diff --git a/backend/app/assets/LiberationSans-Italic.ttf b/backend/app/assets/LiberationSans-Italic.ttf
new file mode 100644
index 0000000..ebf48bc
Binary files /dev/null and b/backend/app/assets/LiberationSans-Italic.ttf differ
diff --git a/backend/app/assets/LiberationSans-Regular.ttf b/backend/app/assets/LiberationSans-Regular.ttf
new file mode 100644
index 0000000..f524339
Binary files /dev/null and b/backend/app/assets/LiberationSans-Regular.ttf differ
diff --git a/backend/app/assets/dak_logo.png b/backend/app/assets/dak_logo.png
new file mode 100644
index 0000000..a1036f7
Binary files /dev/null and b/backend/app/assets/dak_logo.png differ
diff --git a/backend/app/services/notification_service.py b/backend/app/services/notification_service.py
index 6f7bbe3..50049cb 100644
--- a/backend/app/services/notification_service.py
+++ b/backend/app/services/notification_service.py
@@ -5,8 +5,10 @@ from __future__ import annotations
 import logging
 import smtplib
 from datetime import datetime, timezone
+from email.mime.base import MIMEBase
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
+from email import encoders
 from typing import Optional
 
 from sqlalchemy.orm import Session
@@ -28,21 +30,45 @@ def send_email(
     subject: str,
     body: str,
     html_body: str | None = None,
+    attachments: list[tuple[str, bytes, str]] | None = None,
 ) -> bool:
     """Send an email via SMTP SSL.
 
+    Parameters
+    ----------
+    attachments:
+        Optional list of ``(filename, data, mime_type)`` tuples.
+
     Returns *True* on success, *False* on failure (the error is logged).
     """
     try:
-        msg = MIMEMultipart("alternative")
+        if attachments:
+            msg = MIMEMultipart("mixed")
+            text_part = MIMEMultipart("alternative")
+            text_part.attach(MIMEText(body, "plain"))
+            if html_body:
+                text_part.attach(MIMEText(html_body, "html"))
+            msg.attach(text_part)
+
+            for filename, data, mime_type in attachments:
+                maintype, subtype = mime_type.split("/", 1)
+                part = MIMEBase(maintype, subtype)
+                part.set_payload(data)
+                encoders.encode_base64(part)
+                part.add_header(
+                    "Content-Disposition", "attachment", filename=filename
+                )
+                msg.attach(part)
+        else:
+            msg = MIMEMultipart("alternative")
+            msg.attach(MIMEText(body, "plain"))
+            if html_body:
+                msg.attach(MIMEText(html_body, "html"))
+
         msg["From"] = settings.SMTP_FROM
         msg["To"] = to
         msg["Subject"] = subject
 
-        msg.attach(MIMEText(body, "plain"))
-        if html_body:
-            msg.attach(MIMEText(html_body, "html"))
-
         with smtplib.SMTP_SSL(settings.SMTP_HOST, settings.SMTP_PORT) as server:
             server.login(settings.SMTP_USER, settings.SMTP_PASSWORD)
             server.send_message(msg)
diff --git a/backend/app/services/pdf_guide.py b/backend/app/services/pdf_guide.py
new file mode 100644
index 0000000..903b525
--- /dev/null
+++ b/backend/app/services/pdf_guide.py
@@ -0,0 +1,239 @@
+"""PDF guide generator for DAK onboarding invitations."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from fpdf import FPDF
+
+ASSETS_DIR = Path(__file__).resolve().parent.parent / "assets"
+LOGO_PATH = ASSETS_DIR / "dak_logo.png"
+FONT_DIR = ASSETS_DIR
+
+# Font family name used throughout the PDF
+_FONT = "LiberationSans"
+
+# Colours (DAK blue tones)
+DAK_BLUE = (0, 82, 147)
+DAK_DARK = (33, 37, 41)
+DAK_GREY = (108, 117, 125)
+DAK_LIGHT_BG = (240, 244, 248)
+
+
+class _GuidePDF(FPDF):
+    """Custom FPDF subclass with shared header/footer styling."""
+
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+        # Register Liberation Sans (Unicode TTF) in Regular, Bold, Italic
+        self.add_font(_FONT, "", str(FONT_DIR / "LiberationSans-Regular.ttf"))
+        self.add_font(_FONT, "B", str(FONT_DIR / "LiberationSans-Bold.ttf"))
+        self.add_font(_FONT, "I", str(FONT_DIR / "LiberationSans-Italic.ttf"))
+
+    def header(self):
+        if self.page_no() == 1:
+            return  # Page 1 has its own header with logo
+        self.set_font(_FONT, "I", 8)
+        self.set_text_color(*DAK_GREY)
+        self.cell(0, 8, "DAK Zweitmeinungs-Portal \u2014 Anleitung", align="R")
+        self.ln(12)
+
+    def footer(self):
+        self.set_y(-15)
+        self.set_font(_FONT, "I", 8)
+        self.set_text_color(*DAK_GREY)
+        self.cell(0, 10, f"Seite {self.page_no()}/{{nb}}", align="C")
+
+    # -- helpers ---------------------------------------------------------------
+
+    def section_title(self, text: str) -> None:
+        self.set_font(_FONT, "B", 14)
+        self.set_text_color(*DAK_BLUE)
+        self.cell(0, 10, text)
+        self.ln(8)
+        # blue underline
+        self.set_draw_color(*DAK_BLUE)
+        self.set_line_width(0.5)
+        self.line(self.l_margin, self.get_y(), self.w - self.r_margin, self.get_y())
+        self.ln(6)
+
+    def body_text(self, text: str) -> None:
+        self.set_font(_FONT, "", 10)
+        self.set_text_color(*DAK_DARK)
+        self.multi_cell(0, 6, text)
+        self.ln(2)
+
+    def numbered_step(self, number: int, text: str) -> None:
+        self.set_font(_FONT, "B", 10)
+        self.set_text_color(*DAK_BLUE)
+        self.cell(8, 6, f"{number}.")
+        self.set_font(_FONT, "", 10)
+        self.set_text_color(*DAK_DARK)
+        self.multi_cell(0, 6, text)
+        self.ln(1)
+
+    def bullet_item(self, title: str, description: str) -> None:
+        self.set_font(_FONT, "B", 10)
+        self.set_text_color(*DAK_DARK)
+        self.cell(4, 6, "\u2022 ")
+        self.cell(0, 6, title)
+        self.ln(6)
+        if description:
+            self.set_font(_FONT, "", 9)
+            self.set_text_color(*DAK_GREY)
+            self.set_x(self.l_margin + 6)
+            self.multi_cell(0, 5, description)
+            self.ln(2)
+
+    def info_box(self, text: str) -> None:
+        self.set_fill_color(*DAK_LIGHT_BG)
+        self.set_draw_color(*DAK_BLUE)
+        x = self.l_margin
+        y = self.get_y()
+        w = self.w - self.l_margin - self.r_margin
+        self.set_font(_FONT, "", 9)
+        self.set_text_color(*DAK_DARK)
+        # calculate height
+        self.set_xy(x + 4, y + 4)
+        self.multi_cell(w - 8, 5, text)
+        h = self.get_y() - y + 4
+        # draw box behind
+        self.rect(x, y, w, h, style="DF")
+        # re-render text on top
+        self.set_xy(x + 4, y + 4)
+        self.multi_cell(w - 8, 5, text)
+        self.ln(4)
+
+
+def generate_guide_pdf(invite_url: str) -> bytes:
+    """Generate the DAK onboarding guide as PDF bytes.
+
+    Parameters
+    ----------
+    invite_url:
+        The personalised invitation/registration URL to embed in the document.
+
+    Returns
+    -------
+    bytes
+        The raw PDF content (no disk I/O).
+    """
+    pdf = _GuidePDF(orientation="P", unit="mm", format="A4")
+    pdf.alias_nb_pages()
+    pdf.set_auto_page_break(auto=True, margin=20)
+    pdf.set_left_margin(20)
+    pdf.set_right_margin(20)
+
+    # ── Page 1: Welcome & Registration ────────────────────────────────────
+    pdf.add_page()
+
+    # Logo
+    if LOGO_PATH.exists():
+        pdf.image(str(LOGO_PATH), x=75, y=15, w=60)
+        pdf.ln(50)
+    else:
+        pdf.ln(15)
+
+    # Title
+    pdf.set_font(_FONT, "B", 20)
+    pdf.set_text_color(*DAK_BLUE)
+    pdf.cell(0, 12, "Willkommen im", align="C")
+    pdf.ln(12)
+    pdf.cell(0, 12, "DAK Zweitmeinungs-Portal", align="C")
+    pdf.ln(20)
+
+    # Registration section
+    pdf.section_title("Konto erstellen")
+    pdf.body_text(
+        "Um Ihr Konto zu erstellen, folgen Sie bitte diesen Schritten:"
+    )
+
+    pdf.numbered_step(1, "Registrierungslink im Browser öffnen (siehe unten)")
+    pdf.numbered_step(2, "Benutzername festlegen (mindestens 3 Zeichen)")
+    pdf.numbered_step(3, "E-Mail-Adresse eingeben")
+    pdf.numbered_step(4, "Passwort setzen (mindestens 8 Zeichen)")
+    pdf.numbered_step(5, "\u201eRegistrieren\u201c anklicken")
+    pdf.ln(2)
+
+    # Invite URL box
+    pdf.set_font(_FONT, "B", 10)
+    pdf.set_text_color(*DAK_BLUE)
+    pdf.cell(0, 6, "Ihr Registrierungslink:")
+    pdf.ln(7)
+    pdf.info_box(invite_url)
+
+    # First login
+    pdf.section_title("Erste Anmeldung")
+    pdf.body_text(
+        "Melden Sie sich mit Ihrem Benutzernamen (oder E-Mail-Adresse) "
+        "und dem gewählten Passwort an."
+    )
+    pdf.body_text(
+        "Empfehlung: Aktivieren Sie die Zwei-Faktor-Authentifizierung "
+        "unter Kontoverwaltung für zusätzliche Sicherheit."
+    )
+
+    # ── Page 2: Feature overview ──────────────────────────────────────────
+    pdf.add_page()
+    pdf.section_title("Funktionsübersicht")
+
+    pdf.body_text(
+        "Das DAK Zweitmeinungs-Portal bietet Ihnen folgende Funktionen:"
+    )
+    pdf.ln(2)
+
+    features = [
+        ("Dashboard", "Übersicht über KPIs, Diagramme und Jahresvergleich."),
+        ("Fälle", "Fallübersicht mit Such- und Filterfunktionen."),
+        ("ICD-Eingabe", "ICD-Codes für Fälle erfassen und bearbeiten."),
+        ("Berichte", "Wochenberichte als Excel-Datei herunterladen."),
+        (
+            "Wochenübersicht",
+            "Datenübersicht pro Kalenderwoche und ICD-Upload per Excel.",
+        ),
+        (
+            "Freigaben",
+            "Personenbezogene Daten bei Bedarf anfordern (24 Stunden Gültigkeit).",
+        ),
+        (
+            "Kontoverwaltung",
+            "Profil bearbeiten, Passwort ändern, Zwei-Faktor-Authentifizierung.",
+        ),
+    ]
+    for title, desc in features:
+        pdf.bullet_item(title, desc)
+
+    # ── Page 3: Closing notes ─────────────────────────────────────────────
+    pdf.add_page()
+    pdf.section_title("Weitere Informationen")
+
+    pdf.body_text(
+        "Ausführliche Anleitungen zu allen Funktionen finden Sie direkt "
+        "im Portal unter dem Menüpunkt \u201eAnleitung\u201c."
+    )
+    pdf.ln(4)
+
+    pdf.body_text(
+        "Bei Fragen oder Problemen wenden Sie sich bitte an Ihren "
+        "Ansprechpartner bei Complex Care Solutions:"
+    )
+    pdf.ln(2)
+
+    pdf.set_font(_FONT, "B", 10)
+    pdf.set_text_color(*DAK_DARK)
+    pdf.cell(0, 6, "Complex Care Solutions GmbH")
+    pdf.ln(6)
+    pdf.set_font(_FONT, "", 10)
+    pdf.cell(0, 6, "E-Mail: info@complexcaresolutions.de")
+    pdf.ln(6)
+    pdf.cell(0, 6, "Portal: https://dak.complexcaresolutions.de")
+    pdf.ln(16)
+
+    # Final info box
+    pdf.info_box(
+        "Dieses Dokument wurde automatisch generiert und enthält "
+        "Ihren persönlichen Registrierungslink. "
+        "Bitte geben Sie diesen Link nicht an Dritte weiter."
+    )
+
+    return pdf.output()
diff --git a/backend/requirements.txt b/backend/requirements.txt
index d36e458..072ab50 100644
--- a/backend/requirements.txt
+++ b/backend/requirements.txt
@@ -16,6 +16,7 @@ pydantic==2.10.4
 pydantic-settings==2.7.1
 python-dotenv==1.0.1
 email-validator==2.2.0
+fpdf2==2.8.3
 httpx==0.28.1
 
 # Dev/Test