How to determine the project type in Visual Studio?

If the .csproj file has no <ProjectTypeGuids>

As Alex McMillan has pointed out, you could not be able to find the <ProjectTypeGuids> element.

The first answer is correct, except for .dll Library Projects, Console Applications and WinForms Applications as far I know.

They contain <OutputType> (followed by: Library or Exe or WinExe)

and do not contain <ProjectTypeGuids>.

One simple trick is drag and drop project file in notepad and where you can see this kind of stuff<

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>`enter code here`
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">x86</Platform>
    <ProductVersion>8.0.30703</ProductVersion>
    <SchemaVersion>2.0</SchemaVersion>
    <ProjectGuid>{27F8327B-239F-4125-809C-13FB6209D2E3}</ProjectGuid>
    <OutputType>WinExe</OutputType>`enter code here`
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>WpfApplication1</RootNamespace>
    <AssemblyName>WpfApplication1</AssemblyName>
    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
    <TargetFrameworkProfile>Client</TargetFrameworkProfile>
    <FileAlignment>512</FileAlignment>
    <ProjectTypeGuids>{60dc8134-eba5-43b8-bcc9-bb4bc16c2548};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
    <WarningLevel>4</WarningLevel>
  </PropertyGroup>

Compare "ProjectTypeGuid" with this Link. by changing this guid you can add WPF window to WinForms project.