<Frame x:Name="Frame" Source="Page1.xaml" />

        public void openDialogFile (string type)
        {
            OpenFileDialog file = new OpenFileDialog();
            file.Multiselect = false;
            file.Filter = type;
            //type = Text files (*.txt)|*.txt|All files (*.*)|*.*
            file.ShowDialog();
        }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.IO;//потрібно підключати для створення папки чи файла
using System.Windows.Forms;//потрібно додати силку на збірку

namespace Grand_Tomb
{
    /// <summary>
    /// Логика взаимодействия для Page3.xaml
    /// </summary>
    public partial class Page3 : Page
    {
        public Page3()
        {
            InitializeComponent();
        }

        private void ProgressBar_ValueChanged_1(object sender, RoutedPropertyChangedEventArgs<double> e)
        {

        }

        public string openDialogFile (string type)
        {
            OpenFileDialog file = new OpenFileDialog();
            file.Multiselect = false;
            file.Filter = type;
            //type = Text files (*.txt)|*.txt|All files (*.*)|*.*
            file.ShowDialog();
        }

        private void next(object sender, RoutedEventArgs e)
        {
            //считуємо число замовлень
            string sizeString;
            int sizeInt;
            FileStream f = new FileStream("d:\\customers\\The number of buyers.txt", FileMode.Open);//відкриваємо файл
            StreamReader s = new StreamReader(f, Encoding.UTF8);
            sizeString = s.ReadLine();//зчитуємо строку
            sizeInt = int.Parse(sizeString);//конвертуємо string в int
            f.Close();//закриваємо потік

            //File.CreateText("d:\\customers\\" + (sizeInt + 1) + "\\Надгробний пам'ятник.txt"); //створюємo файл
            File.AppendAllText(@"d:\\customers\\" + (sizeInt + 1) + "\\Надгробний пам'ятник.docx", otherText.Text + "\n");

            this.NavigationService.Navigate(new Uri("Coffin_1.xaml", UriKind.Relative));
        }

        private void photoClick(object sender, RoutedEventArgs e)
        {
            openDialogFile("Image Files(*.BMP;*.JPG;*.GIF;*.PNG)|*.BMP;*.JPG;*.GIF;*.PNG|All files (*.*)|*.*");
        }

        private void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
        {

        }

        private void ago(object sender, RoutedEventArgs e)
        {
            this.NavigationService.Navigate(new Uri("TypeMonument.xaml", UriKind.Relative));
        }

        private void showMonument(object sender, RoutedEventArgs e)
        {
            this.NavigationService.Navigate(new Uri("ShowMonument.xaml", UriKind.Relative));
        }


        private void monumentClick(object sender, RoutedEventArgs e)
        {
            openDialogFile("Image Files(*.BMP;*.JPG;*.GIF;*.PNG)|*.BMP;*.JPG;*.GIF;*.PNG|All files (*.*)|*.*");
        }

        private void typeGraniteClick(object sender, RoutedEventArgs e)
        {
            openDialogFile("Image Files(*.BMP;*.JPG;*.GIF;*.PNG)|*.BMP;*.JPG;*.GIF;*.PNG|All files (*.*)|*.*");
        }

        private void designElementsClick(object sender, RoutedEventArgs e)
        {
            openDialogFile("Image Files(*.BMP;*.JPG;*.GIF;*.PNG)|*.BMP;*.JPG;*.GIF;*.PNG|All files (*.*)|*.*");
        }
    }
}