diff --git a/app/controllers/collection_resources_controller.rb b/app/controllers/collection_resources_controller.rb
index 3bec72371..266be6d39 100644
--- a/app/controllers/collection_resources_controller.rb
+++ b/app/controllers/collection_resources_controller.rb
@@ -52,6 +52,10 @@ class CollectionResourcesController < ApplicationController
     @collection_resource = MandatoryCollectionResourcesService.generate_resource(log_type, year, resource_type)
     render_not_found unless @collection_resource
 
+    validate_file(file)
+
+    return render "collection_resources/edit" if @collection_resource.errors.any?
+
     filename = @collection_resource.download_filename
     begin
       UploadCollectionResourcesService.upload_collection_resource(filename, file)
@@ -95,4 +99,23 @@ private
   def resource_for_year_can_be_updated?(year)
     editable_collection_resource_years.include?(year)
   end
+
+  def validate_file(file)
+    return @collection_resource.errors.add(:file, "Select which file to upload") unless file
+    return @collection_resource.errors.add(:file, "The file is above 100MB") if file.size > 100.megabytes
+
+    argv = %W[file --brief --mime-type -- #{file.path}]
+    output = `#{argv.shelljoin}`
+
+    case @collection_resource.resource_type
+    when "paper_form"
+      unless output.match?(/application\/pdf/)
+        @collection_resource.errors.add(:file, "The paper form must be a PDF.")
+      end
+    when "bulk_upload_template", "bulk_upload_specification"
+      unless output.match?(/application\/vnd\.ms-excel|application\/vnd\.openxmlformats-officedocument\.spreadsheetml\.sheet/)
+        @collection_resource.errors.add(:file, "The #{@collection_resource.short_display_name.downcase} must be a Microsoft Excel file.")
+      end
+    end
+  end
 end
diff --git a/app/models/collection_resource.rb b/app/models/collection_resource.rb
index 442594d8c..d5c3c895b 100644
--- a/app/models/collection_resource.rb
+++ b/app/models/collection_resource.rb
@@ -2,7 +2,7 @@ class CollectionResource
   include ActiveModel::Model
   include Rails.application.routes.url_helpers
 
-  attr_accessor :resource_type, :display_name, :short_display_name, :year, :log_type, :download_filename
+  attr_accessor :resource_type, :display_name, :short_display_name, :year, :log_type, :download_filename, :file
 
   def download_path
     download_mandatory_collection_resource_path(log_type:, year:, resource_type:)
diff --git a/spec/features/collection_resources_spec.rb b/spec/features/collection_resources_spec.rb
new file mode 100644
index 000000000..306b4355d
--- /dev/null
+++ b/spec/features/collection_resources_spec.rb
@@ -0,0 +1,142 @@
+require "rails_helper"
+
+RSpec.describe "Collection resources" do
+  let(:user) { create(:user, :support) }
+
+  before do
+    allow(user).to receive(:need_two_factor_authentication?).and_return(false)
+    sign_in user
+  end
+
+  context "when uploading paper form" do
+    it "only allows pdf files for lettings" do
+      visit("/collection-resources/lettings/2024/paper_form/edit")
+
+      click_button("Save changes")
+
+      expect(page).to have_content("Select which file to upload")
+
+      expect(page).to have_content("Change the paper form")
+      expect(page).to have_content("Lettings 2024 to 2025")
+
+      attach_file "file", file_fixture("excel_file.xlsx")
+      click_button("Save changes")
+
+      expect(page).to have_content("The paper form must be a PDF.")
+
+      attach_file "file", file_fixture("pdf_file.pdf")
+      click_button("Save changes")
+
+      expect(page).not_to have_content("The paper form must be a PDF.")
+    end
+
+    it "only allows pdf files for sales" do
+      visit("/collection-resources/sales/2024/paper_form/edit")
+
+      click_button("Save changes")
+
+      expect(page).to have_content("Select which file to upload")
+
+      expect(page).to have_content("Change the paper form")
+      expect(page).to have_content("Sales 2024 to 2025")
+
+      attach_file "file", file_fixture("excel_file.xlsx")
+      click_button("Save changes")
+
+      expect(page).to have_content("The paper form must be a PDF.")
+
+      attach_file "file", file_fixture("pdf_file.pdf")
+      click_button("Save changes")
+
+      expect(page).not_to have_content("The paper form must be a PDF.")
+    end
+  end
+
+  context "when uploading bu template" do
+    it "only allows excel files for lettings" do
+      visit("/collection-resources/lettings/2024/bulk_upload_template/edit")
+
+      click_button("Save changes")
+
+      expect(page).to have_content("Select which file to upload")
+
+      expect(page).to have_content("Change the bulk upload template")
+      expect(page).to have_content("Lettings 2024 to 2025")
+
+      attach_file "file", file_fixture("pdf_file.pdf")
+      click_button("Save changes")
+
+      expect(page).to have_content("The bulk upload template must be a Microsoft Excel file.")
+
+      attach_file "file", file_fixture("excel_file.xlsx")
+      click_button("Save changes")
+
+      expect(page).not_to have_content("The bulk upload template must be a Microsoft Excel file.")
+    end
+
+    it "only allows excel files for sales" do
+      visit("/collection-resources/sales/2024/bulk_upload_template/edit")
+
+      click_button("Save changes")
+
+      expect(page).to have_content("Select which file to upload")
+
+      expect(page).to have_content("Change the bulk upload template")
+      expect(page).to have_content("Sales 2024 to 2025")
+
+      attach_file "file", file_fixture("pdf_file.pdf")
+      click_button("Save changes")
+
+      expect(page).to have_content("The bulk upload template must be a Microsoft Excel file.")
+
+      attach_file "file", file_fixture("excel_file.xlsx")
+      click_button("Save changes")
+
+      expect(page).not_to have_content("The bulk upload template must be a Microsoft Excel file.")
+    end
+  end
+
+  context "when uploading bu specification" do
+    it "only allows excel files for lettings" do
+      visit("/collection-resources/lettings/2024/bulk_upload_specification/edit")
+
+      click_button("Save changes")
+
+      expect(page).to have_content("Select which file to upload")
+
+      expect(page).to have_content("Change the bulk upload specification")
+      expect(page).to have_content("Lettings 2024 to 2025")
+
+      attach_file "file", file_fixture("pdf_file.pdf")
+      click_button("Save changes")
+
+      expect(page).to have_content("The bulk upload specification must be a Microsoft Excel file.")
+
+      attach_file "file", file_fixture("excel_file.xlsx")
+      click_button("Save changes")
+
+      expect(page).not_to have_content("The bulk upload specification must be a Microsoft Excel file.")
+    end
+
+    it "only allows excel files for sales" do
+      visit("/collection-resources/sales/2024/bulk_upload_specification/edit")
+
+      click_button("Save changes")
+
+      expect(page).to have_content("Select which file to upload")
+
+      expect(page).to have_content("Change the bulk upload specification")
+      expect(page).to have_content("Sales 2024 to 2025")
+
+      attach_file "file", file_fixture("pdf_file.pdf")
+      click_button("Save changes")
+
+      expect(page).to have_content("The bulk upload specification must be a Microsoft Excel file.")
+
+      attach_file "file", file_fixture("excel_file.xlsx")
+      click_button("Save changes")
+
+      expect(page).not_to have_content("The bulk upload specification must be a Microsoft Excel file.")
+    end
+  end
+end
diff --git a/spec/fixtures/files/excel_file.xlsx b/spec/fixtures/files/excel_file.xlsx
new file mode 100644
index 000000000..dcc5aaaf3
Binary files /dev/null and b/spec/fixtures/files/excel_file.xlsx differ
diff --git a/spec/fixtures/files/pdf_file.pdf b/spec/fixtures/files/pdf_file.pdf
new file mode 100644
index 000000000..65a01d0a9
Binary files /dev/null and b/spec/fixtures/files/pdf_file.pdf differ