Use first argument as file. Set initial browser directory as the current one.

FrmCsvViewer.cs

@@ -16,6 +16,7 @@ namespace CsvView
         private void txtPath_DoubleClick(object sender, EventArgs e)
         {
             OpenFileDialog loadDialog = new OpenFileDialog();
+            loadDialog.InitialDirectory = Path.GetDirectoryName(System.Reflection.Assembly.GetEntryAssembly().Location);
             DialogResult result = loadDialog.ShowDialog();
             if (result == DialogResult.OK)
             {
@@ -40,7 +41,13 @@ namespace CsvView
                 return;
             }
 
-            _loadedFile = txtPath.Text;
+            LoadFile(txtPath.Text);
+        }
+
+        public void LoadFile(string fileName)
+        {
+            _loadedFile = fileName;
+            txtPath.Text = fileName;
             DateTime dtFile = File.GetCreationTime(_loadedFile);
             string indexFile = _loadedFile + ".idx";
             if (File.Exists(indexFile) && File.GetCreationTime(indexFile) > dtFile)

Program.cs

@@ -1,22 +1,25 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
 using System.Windows.Forms;
 
 namespace CsvView.Net
 {
     static class Program
     {
-        /// <summary>
-        /// The main entry point for the application.
-        /// </summary>
         [STAThread]
-        static void Main()
+        static void Main(string[] args)
         {
             Application.EnableVisualStyles();
             Application.SetCompatibleTextRenderingDefault(false);
-            Application.Run(new FrmCsvViewer());
+
+            var frmCsvViewer = new FrmCsvViewer();
+            if (args.Length > 0)
+            {
+                if (System.IO.File.Exists(args[0]))
+                {
+                    frmCsvViewer.LoadFile(args[0]);
+                }
+            }
+            Application.Run(frmCsvViewer);
         }
     }
 }