diff --git a/src/controller.py b/src/controller.py
index d31ec9c..7bc315c 100644
--- a/src/controller.py
+++ b/src/controller.py
@@ -1,11 +1,25 @@
+from src.template_mapper import TemplateMapper
+from src.validation import validate_extracted_data
 from src.file_manipulator import FileManipulator
 
 class Controller:
     def __init__(self):
         self.file_manipulator = FileManipulator()
-
+        self.mapper = TemplateMapper({
+        "patient_name": "NameField",
+        "age": "AgeField",
+        "diagnosis": "DiagnosisField"
+})
+    def map_data(self, validated_data: dict):
+    return self.mapper.map_to_pdf_fields(validated_data)
+    
     def fill_form(self, user_input: str, fields: list, pdf_form_path: str):
-        return self.file_manipulator.fill_form(user_input, fields, pdf_form_path)
+    data = self.file_manipulator.fill_form(user_input, fields, pdf_form_path)
+
+    if not validate_extracted_data(data):
+        raise ValueError("Invalid extracted data")
+
+    return data
     
     def create_template(self, pdf_path: str):
-        return self.file_manipulator.create_template(pdf_path)
\ No newline at end of file
+        return self.file_manipulator.create_template(pdf_path)
diff --git a/src/schema.py b/src/schema.py
new file mode 100644
index 0000000..ba1866c
--- /dev/null
+++ b/src/schema.py
@@ -0,0 +1,7 @@
+REQUIRED_FIELDS = {
+    "incident_type": str,
+    "location": str,
+    "incident_time": str,
+    "units_involved": list,
+    "summary": str
+}
diff --git a/src/template_mapper.py b/src/template_mapper.py
new file mode 100644
index 0000000..7e458d8
--- /dev/null
+++ b/src/template_mapper.py
@@ -0,0 +1,15 @@
+class TemplateMapper:
+    def __init__(self, mapping_config: dict):
+        """
+        mapping_config: dict mapping JSON fields → PDF field names
+        """
+        self.mapping = mapping_config
+
+    def map_to_pdf_fields(self, structured_data: dict) -> dict:
+        mapped_data = {}
+
+        for json_field, pdf_field in self.mapping.items():
+            if json_field in structured_data:
+                mapped_data[pdf_field] = structured_data[json_field]
+
+        return mapped_data
diff --git a/src/validation.py b/src/validation.py
new file mode 100644
index 0000000..eeaa16c
--- /dev/null
+++ b/src/validation.py
@@ -0,0 +1,11 @@
+from src.schema import REQUIRED_FIELDS
+
+def validate_extracted_data(data: dict) -> bool:
+    for field, field_type in REQUIRED_FIELDS.items():
+        if field not in data:
+            return False
+        if not isinstance(data[field], field_type):
+            return False
+        if data[field] in ["", None]:
+            return False
+    return True
diff --git a/tests/src/tests/test_controller.py b/tests/src/tests/test_controller.py
new file mode 100644
index 0000000..a182333
--- /dev/null
+++ b/tests/src/tests/test_controller.py
@@ -0,0 +1,16 @@
+from src.controller import Controller
+
+
+def test_fill_form_validation_fail(monkeypatch):
+    controller = Controller()
+
+    def mock_fill_form(user_input, fields, pdf_form_path):
+        return {"patient_name": "", "age": 30, "diagnosis": "Flu"}
+
+    monkeypatch.setattr(controller.file_manipulator, "fill_form", mock_fill_form)
+
+    try:
+        controller.fill_form("input", [], "file.pdf")
+        assert False  # Should not reach here
+    except ValueError:
+        assert True
diff --git a/tests/src/tests/test_validation.py b/tests/src/tests/test_validation.py
new file mode 100644
index 0000000..3ebb8e9
--- /dev/null
+++ b/tests/src/tests/test_validation.py
@@ -0,0 +1,19 @@
+def test_valid_data():
+    data = {
+        "incident_type": "Fire",
+        "location": "Downtown",
+        "incident_time": "2026-03-20 10:00",
+        "units_involved": ["Unit1", "Unit2"],
+        "summary": "Fire contained"
+    }
+    assert validate_extracted_data(data) == True
+
+def test_wrong_type():
+    data = {
+        "incident_type": "Fire",
+        "location": "Downtown",
+        "incident_time": "2026-03-20 10:00",
+        "units_involved": "Unit1",  # should be list
+        "summary": "Fire contained"
+    }
+    assert validate_extracted_data(data) == False
diff --git a/tests/test_template_mapper.py b/tests/test_template_mapper.py
new file mode 100644
index 0000000..27ee868
--- /dev/null
+++ b/tests/test_template_mapper.py
@@ -0,0 +1,43 @@
+from src.template_mapper import TemplateMapper
+
+
+def test_mapping_success():
+    mapping = {
+        "patient_name": "NameField",
+        "age": "AgeField",
+        "diagnosis": "DiagnosisField"
+    }
+
+    data = {
+        "patient_name": "John Doe",
+        "age": 45,
+        "diagnosis": "Burn injury"
+    }
+
+    mapper = TemplateMapper(mapping)
+    result = mapper.map_to_pdf_fields(data)
+
+    assert result == {
+        "NameField": "John Doe",
+        "AgeField": 45,
+        "DiagnosisField": "Burn injury"
+    }
+
+
+def test_missing_fields():
+    mapping = {
+        "patient_name": "NameField",
+        "age": "AgeField",
+        "diagnosis": "DiagnosisField"
+    }
+
+    data = {
+        "patient_name": "John Doe"
+    }
+
+    mapper = TemplateMapper(mapping)
+    result = mapper.map_to_pdf_fields(data)
+
+    assert result == {
+        "NameField": "John Doe"
+    }