Helper code to extract resources from a C# assembly.

ManifestResourceHelper.cs

using System.Collections.Generic;
using System.IO;
using System.Reflection;

namespace YOUR_NAMESPACE
{
    public static class ManifestResourceHelper
    {
        public static string[] GetManifestResourceNames(Assembly asm = null)
        {
            asm = asm ?? Assembly.GetCallingAssembly();

            return asm.GetManifestResourceNames();
        }

        public static IEnumerable<string> GetManifestResourcePaths(Assembly asm = null)
        {
            asm = asm ?? Assembly.GetCallingAssembly();
            return asm.GetManifestResourceNames();
        }

        public static ExcelPackage ExtractExcelPackage(string relativePathToResource)
        {
            var pkg = new ExcelPackage();

            using (var stream = ExtractResourceStream(relativePathToResource))
            {
                pkg.Load(stream);
            }

            return pkg;
        }

        public static FileInfo ExtractResourceToDisk(string relativePathToResource, string targetPathOnDisk = null, bool overwrite = true)
        {
            targetPathOnDisk = targetPathOnDisk ?? Path.GetTempFileName();
            var file = new FileInfo(targetPathOnDisk);
            if (File.Exists(file.FullName) && overwrite)
            {
                File.Delete(file.FullName);
            }

            var stream = ExtractResourceStream(relativePathToResource, Assembly.GetCallingAssembly());
            var content = StreamToContentString(stream);

            File.WriteAllText(file.FullName, content);
            return file;
        }

        public static Stream ExtractResourceStream(string relativePathToResource, Assembly asm = null)
        {
            return GetManifestResourceStream(relativePathToResource, asm);
        }

        private static string GetFullResourceName(string relativePathToResource, Assembly asm = null)
        {
            asm = asm ?? Assembly.GetCallingAssembly();
            return asm.GetName().Name + "." + relativePathToResource.Replace('/', '\\').Replace('\\', '.');
        }

        private static Stream GetManifestResourceStream(string resourceName, Assembly asm)
        {
            asm = asm ?? Assembly.GetCallingAssembly();
            resourceName = GetFullResourceName(resourceName);

            var resourceInfo = asm.GetManifestResourceInfo(resourceName);
            if (resourceInfo == null)
            {
                var message = String.Format("Could not find the requested resource '{0}' among: {1}", resourceName, Environment.NewLine);
                var names = asm.GetManifestResourceNames();
                message += string.Join(";" + Environment.NewLine, names);
                throw new FileNotFoundException(message, resourceName);
            }

            var manifestResourceStream = asm.GetManifestResourceStream(resourceName);
            return manifestResourceStream;
        }

        private static string StreamToContentString(Stream resourceStream)
        {
            if (resourceStream == null) return "";

            using (var reader = new StreamReader(resourceStream))
            {
                return reader.ReadToEnd();
            }
        }
    }
}