Sorry, we couldn't find your file. Was it moved, renamed or deleted?

If you use quotes around the path and name, that will solve your problem:

process.StartInfo.Arguments = this.AddQuotesForWhiteSpace(Path + filename);

public string AddQuotesForWhiteSpace(string path)
{
    return !string.IsNullOrWhiteSpace(path) ? 
        path.Contains(" ") && (!path.StartsWith("\"") && !path.EndsWith("\"")) ? 
            "\"" + path + "\"" : path : 
            string.Empty;
}

Here self I wrote solution

1. When inputting file, remove whitespaces of name and save file in Processed Folder.
2. keep original name with file record.
3. When viewing file on listview Show recorded (real) file name.

It works.

If you have better solution post it. for Education. :D

Hello @Manoj Madushantha

Another way to go is use Path.Combine rather than + when combining path and filename as Path.Combine places \ character where needed. And on Windows 10 I've never seen an issue going this was with spaces in folder and/or file name. Note in the two code samples below you can write less code to achieve the same as what you had.

Alternate to Application.StartupPath

private static string _basePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Processed");  

C# 9 example

public class CodeSample  
{  
    private static string _basePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Processed");  
    public static void Demo(string filename, string extention)  
    {  
         
        var process = new Process();  
  
        process.StartInfo.FileName = extention switch  
        {  
            "docx" => "WINWORD.EXE",  
            "doc" => "WINWORD.EXE",  
            "xlsx" => "EXCEL.EXE",  
            "xls" => "EXCEL.EXE",  
            "pdf" => "AcroRd32.exe",  
            _ => throw new NotImplementedException("Unknown file type")  
        };  
  
         
        if (!File.Exists(Path.Combine(_basePath, filename))) return;  
          
        process.StartInfo.Arguments = Path.Combine(_basePath, filename);  
        process.Start();  
  
  
    }  
}  

Prior to C# 9

public class CodeSample  
{  
    private static string _basePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Processed");  
    public static void Demo(string filename, string extention)  
    {  
         
        var process = new Process();  
  
        switch (extention)  
        {  
            case "docx":  
            case "doc":  
                process.StartInfo.FileName = "WINWORD.EXE";  
                break;  
            case "xlsx":  
            case "xls":  
                process.StartInfo.FileName = "EXCEL.EXE";  
                break;  
            case "pdf":  
                process.StartInfo.FileName = "AcroRd32.exe";  
                break;  
            default:  
                throw new NotImplementedException("Unknown file type");  
        }  
  
        if (!File.Exists(Path.Combine(_basePath, filename))) return;  
          
        process.StartInfo.Arguments = Path.Combine(_basePath, filename);  
        process.Start();  
  
  
    }  
}