diff --git a/app/models/budget/investment.rb b/app/models/budget/investment.rb
index 44cc10936..1fb0c1b26 100644
--- a/app/models/budget/investment.rb
+++ b/app/models/budget/investment.rb
@@ -7,13 +7,14 @@ class Budget
     include Reclassification
     include Followable
     include Documentable
+    documentable max_documents_allowed: 3,
+                 max_file_size: 3.megabytes,
+                 accepted_content_types: [ "application/pdf" ]
 
     acts_as_votable
     acts_as_paranoid column: :hidden_at
     include ActsAsParanoidAliases
 
-    MAX_DOCUMENTS_SIZE = 3
-    
     belongs_to :author, -> { with_hidden }, class_name: 'User', foreign_key: 'author_id'
     belongs_to :heading
     belongs_to :group
diff --git a/app/models/concerns/documentable.rb b/app/models/concerns/documentable.rb
index 82c6c0b6e..4aeaf6eab 100644
--- a/app/models/concerns/documentable.rb
+++ b/app/models/concerns/documentable.rb
@@ -5,4 +5,16 @@ module Documentable
     has_many :documents, as: :documentable, dependent: :destroy
   end
 
+  module ClassMethods
+    attr_reader :max_documents_allowed, :max_file_size, :accepted_content_types
+
+    private
+
+    def documentable(options= {})
+      @max_documents_allowed = options[:max_documents_allowed]
+      @max_file_size = options[:max_file_size]
+      @accepted_content_types = options[:accepted_content_types]
+    end
+  end
+
 end
diff --git a/app/models/document.rb b/app/models/document.rb
index 688540c09..0c48edbba 100644
--- a/app/models/document.rb
+++ b/app/models/document.rb
@@ -4,12 +4,36 @@ class Document < ActiveRecord::Base
   belongs_to :user
   belongs_to :documentable, polymorphic: true
 
-  validates_attachment :attachment, presence: true,
-    content_type: { content_type: "application/pdf" },
-    size: { in: 0..3.megabytes }
+  validates_attachment :attachment, presence: true
+  do_not_validate_attachment_file_type :attachment
+  validate :validate_attachment_content_type
+
+  validate :validate_attachment_size
   validates :title, presence: true
   validates :user, presence: true
   validates :documentable_id, presence: true
   validates :documentable_type, presence: true
 
+  def validate_attachment_size
+    if attachment.file? && documentable.present? && attachment_file_size > documentable.class.max_file_size
+      errors[:attachment] = I18n.t("documents.errors.messages.in_between",
+                                    min: "0 Bytes",
+                                    max: "#{bytesToMeg(documentable.class.max_file_size)} MB")
+    end
+  end
+
+  def validate_attachment_content_type
+    if attachment.file? && documentable.present? && !documentable.class.accepted_content_types.include?(attachment_content_type)
+      errors[:attachment] = I18n.t("documents.errors.messages.content_type",
+                                    content_type: attachment_content_type,
+                                    accepted_content_types: documentable.class.accepted_content_types.join(", "))
+    end
+  end
+
+  private
+
+    def bytesToMeg bytes
+      bytes / (1024.0 * 1024.0)
+    end
+
 end
diff --git a/app/models/proposal.rb b/app/models/proposal.rb
index 9e0e0e96a..e780dd21b 100644
--- a/app/models/proposal.rb
+++ b/app/models/proposal.rb
@@ -10,12 +10,14 @@ class Proposal < ActiveRecord::Base
   include Graphqlable
   include Followable
   include Documentable
+  documentable max_documents_allowed: 3,
+               max_file_size: 3.megabytes,
+               accepted_content_types: [ "application/pdf" ]
 
   acts_as_votable
   acts_as_paranoid column: :hidden_at
   include ActsAsParanoidAliases
 
-  MAX_DOCUMENTS_SIZE = 3
   RETIRE_OPTIONS = %w(duplicated started unfeasible done other)
 
   belongs_to :author, -> { with_hidden }, class_name: 'User', foreign_key: 'author_id'
diff --git a/app/views/budgets/investments/_investment_show.html.erb b/app/views/budgets/investments/_investment_show.html.erb
index 7017e22e0..3f1890ae8 100644
--- a/app/views/budgets/investments/_investment_show.html.erb
+++ b/app/views/budgets/investments/_investment_show.html.erb
@@ -4,7 +4,7 @@
     <div class="small-12 medium-9 column">
       <%= back_link_to budget_investments_path(investment.budget, heading_id: investment.heading) %>
 
-      <% if can?(:create, @document) && investment.documents.size < Budget::Investment::MAX_DOCUMENTS_SIZE %>
+      <% if can?(:create, @document) && investment.documents.size < Budget::Investment.max_documents_allowed %>
         <%= link_to t("documents.upload_document"),
                     new_document_path(documentable_id:investment, documentable_type: investment.class.name, from: request.url),
                     class: 'button hollow float-right' %>
diff --git a/app/views/budgets/investments/show.html.erb b/app/views/budgets/investments/show.html.erb
index 37565eadd..e55e88510 100644
--- a/app/views/budgets/investments/show.html.erb
+++ b/app/views/budgets/investments/show.html.erb
@@ -23,7 +23,7 @@
   <div class="tabs-panel" id="tab-documents">
     <%= render 'documents/documents',
                 documents: @investment.documents,
-                max_documents_size: Budget::Investment::MAX_DOCUMENTS_SIZE %>
+                max_documents_allowed: Budget::Investment.max_documents_allowed %>
   </div>
 
 </div>
diff --git a/app/views/documents/_documents.html.erb b/app/views/documents/_documents.html.erb
index e9bac2505..3f5a47adc 100644
--- a/app/views/documents/_documents.html.erb
+++ b/app/views/documents/_documents.html.erb
@@ -1,10 +1,10 @@
 <% if documents.any? %>
 
-  <% if documents.size == max_documents_size %>
+  <% if documents.size == max_documents_allowed %>
     <div class="row documents-list">
       <div class="small-12 column">
         <div class="callout primary text-center">
-          <%= t "documents.max_documents_size_reached" %>
+          <%= t "documents.max_documents_allowed_reached" %>
         </div>
       </div>
     </div>
diff --git a/app/views/proposals/show.html.erb b/app/views/proposals/show.html.erb
index 62c7f4314..e75f80dd6 100644
--- a/app/views/proposals/show.html.erb
+++ b/app/views/proposals/show.html.erb
@@ -16,7 +16,7 @@
       <div class="small-12 medium-9 column">
         <%= back_link_to %>
 
-        <% if can?(:create, @document) && @proposal.documents.size < Proposal::MAX_DOCUMENTS_SIZE %>
+        <% if can?(:create, @document) && @proposal.documents.size < Proposal.max_documents_allowed %>
           <%= link_to t("documents.upload_document"),
                       new_document_path(documentable_id: @proposal, documentable_type: @proposal.class.name, from: request.url),
                       class: 'button hollow float-right' %>
@@ -166,6 +166,6 @@
   <div class="tabs-panel" id="tab-documents">
     <%= render 'documents/documents',
                 documents: @proposal.documents,
-                max_documents_size: Proposal::MAX_DOCUMENTS_SIZE %>
+                max_documents_allowed: Proposal.max_documents_allowed %>
   </div>
 </div>
diff --git a/config/locales/en/documents.yml b/config/locales/en/documents.yml
index b4a614516..8a81861ca 100644
--- a/config/locales/en/documents.yml
+++ b/config/locales/en/documents.yml
@@ -3,7 +3,7 @@ en:
     tab: Documents
     no_documents: Don't have uploaded documents
     upload_document: Upload document
-    max_documents_size_reached: You have reached the maximum number of documents allowed! You have to delete one before you can upload another.
+    max_documents_allowed_reached: You have reached the maximum number of documents allowed! You have to delete one before you can upload another.
     form:
       attachment_label: Choose attachment file
       submit_button: Upload document
@@ -24,3 +24,7 @@ en:
       download_document: Download PDF
       destroy_document: Destroy
       link_document: Link
+    errors:
+      messages:
+        in_between: must be in between %{min} and %{max}
+        wrong_content_type: content type %{content_type} does not match any of accepted content types %{accepted_content_types}
\ No newline at end of file
diff --git a/config/locales/es/documents.yml b/config/locales/es/documents.yml
index e237dee21..3fe544cee 100644
--- a/config/locales/es/documents.yml
+++ b/config/locales/es/documents.yml
@@ -3,7 +3,7 @@ es:
     tab: Documentos
     no_documents: No hay documentos subidos
     upload_document: Subir documento
-    max_documents_size_reached: ¡Has alcanzado el número máximo de documentos permitidos! Tienes que eliminar uno antes de poder subir otro.
+    max_documents_allowed_reached: ¡Has alcanzado el número máximo de documentos permitidos! Tienes que eliminar uno antes de poder subir otro.
     form:
       attachment_label: Selecciona un archivo
       submit_button: Subir documento
@@ -24,3 +24,7 @@ es:
       download_document: Descargar PDF
       destroy_document: Eliminar
       link_document: Enlace
+    errors:
+      messages:
+        in_between: debe estar entre %{min} y %{max}
+        wrong_content_type: El tipo de contenido %{content_type} del archivo no coincide con ninguno de los tipos de contenido aceptados %{accepted_content_types}
\ No newline at end of file
diff --git a/spec/shared/models/document_validations.rb b/spec/shared/models/document_validations.rb
index a5cff53c5..6f85705f4 100644
--- a/spec/shared/models/document_validations.rb
+++ b/spec/shared/models/document_validations.rb
@@ -1,6 +1,8 @@
 shared_examples "document validations" do |documentable_factory|
 
-  let(:document) { build(:document, documentable_factory.to_sym) }
+  let(:document)      { build(:document, documentable_factory.to_sym) }
+  let(:max_file_size) { document.documentable.class.max_file_size }
+  let(:accepted_content_types) { document.documentable.class.accepted_content_types }
 
   it "should be valid" do
     expect(document).to be_valid
@@ -18,17 +20,20 @@ shared_examples "document validations" do |documentable_factory|
     expect(document).to_not be_valid
   end
 
-  it "should not be valid for attachment images" do
-    document.attachment = File.new("spec/fixtures/files/logo_header.png")
+  it "should be valid for all accepted content types" do
+    accepted_content_types.each do |content_type|
+      extension = content_type.split("/").last
+      document.attachment = File.new("spec/fixtures/files/empty.#{extension}")
 
-    expect(document).to_not be_valid
+      expect(document).to be_valid
+    end
   end
 
-  it "should not be valid for attachment 3MB" do
-    document.stub(:attachment_file_size).and_return(3.1.megabytes)
+  it "should not be valid for attachments larger than documentable max_file_size definition" do
+    document.stub(:attachment_file_size).and_return(max_file_size.bytes + 1.byte)
 
-    document.should_not be_valid
-    expect(document.errors[:attachment]).to include "must be in between 0 Bytes and 3 MB"
+    expect(document).to_not be_valid
+    expect(document.errors[:attachment]).to include "must be in between 0 Bytes and #{bytesToMeg(max_file_size)} MB"
   end
 
   it "should not be valid without a user_id" do
@@ -50,3 +55,7 @@ shared_examples "document validations" do |documentable_factory|
   end
 
 end
+
+def bytesToMeg(bytes)
+  bytes / (1024.0 * 1024.0)
+end
\ No newline at end of file