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C# cannot read from read-only Excel file

I have a folder on my PC containing multiple Excel spreadsheets that are all marked as read-only.
The folder is synced to my company's Sharepoint via OneDrive.
When I try to programmatically read data from one of these sheets via Microsoft.Office.Interop.Excel, I keep getting the You cannot use this command on a protected sheet error.
Here's the code I use to open the file:
public ExcelReader(String filePath)
{
this.filePath = filePath;
FileName = filePath.Substring(filePath.LastIndexOf("\\")+1);
app = new Excel.Application();
app.DisplayAlerts = false;
workbook = app.Workbooks.Open(filePath, false, true); //open in read only
}
public void openSheet(String sheet)
{
SheetName = sheet;
worksheet = workbook.Sheets[sheet];
Excel.Range last = worksheet.Cells.SpecialCells(Excel.XlCellType.xlCellTypeLastCell, Type.Missing);
ColumnsTotal = last.Column;
RowsTotal = last.Row;
}
The line that throws the exception is Excel.Range last = worksheet.Cells.SpecialCells(Excel.XlCellType.xlCellTypeLastCell, Type.Missing);.
I figured that since I explicitly tell the Workbook to open in Read-only mode, and since I never modify the content of these files, the fact that files are read-only shouldn't be a problem.
What am I doing wrong here? How do I read the content of these files without unprotecting them (I can't do that for security reasons)?

Establish Connection to existing Excel Application and Run an Excel macro C#

All,
Apologies if this is a very basic question and has been asked before, I predominately write in VBA / JAVA. However a project I am working on requires a C# script. Which carries out 3 simple steps:
Target a excel workbook which is already open. File path:
\Csdatg04\psproject\Robot\Peoplesoft To LV\Master Files - Do not use\Transactions into LV Template.xlsm
Populate cells A1,A2 & A3 with three variables already retrieved earlier in the automation.
Run a macro stored within the filepath mentioned above Macro name "ControlMacroACT"
The code I have developed is below, however in each stage identified above I am encountering errors (Probably basic errors).
Error 1: This line of code is to open a workbook I would like this to target an already active workbook.
Error 2: Worksheet not found
public void RunActualsMacro(string Filepath, string Period, String FiscalYear)
{
//~~> Define your Excel Objects
Excel.Application xlApp = new Excel.Application();
Excel.Workbook xlWorkBook;
//~~> Start Excel and open the workbook.
//Error 1
xlWorkBook = xlApp.Workbooks.Open("\\Csdatg04\\psproject\\Robot\\Peoplesoft To LV\\Master Files - Do not use\\Transactions into LV Template.xlsm");
// Populat Cells A1,A2,A3 with string variables
// Error 2 Worksheet not found
worksheet.Rows.Cells[1, 1] = Filepath;
worksheet.Rows.Cells[2, 1] = Period;
worksheet.Rows.Cells[3, 1] = FiscalYear;
//~~> Run the macro ControlMacroAct
xlApp.Run("ControlMacroACT");
//~~> Clean-up: Close the workbook
xlWorkBook.Close(false);
//~~> Quit the Excel Application
xlApp.Quit();
}
Any help would be much appreciated.

You need to use Marshal.GetActiveObject, and this code is roughly right, but cannot test right now.
public void RunActualsMacro(string Filepath, string Period, String FiscalYear)
{
//~~> Define your Excel Objects
Excel.Application xlApp = null;
Excel.Workbook xlWorkBook;
//~~> Start Excel and open the workbook.
//handle errors below
try {
xlApp = (Excel.Application) System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application");
} catch {
//perhaps exit - or throw??
}
xlWorkBook = xlApp.Workbooks["Transactions into LV Template.xlsm"];
// Populat Cells A1,A2,A3 with string variables
Excel.Worksheet ws = xlWorkBook.Worksheets["Sheet1"] //what the tab name of sheet
ws.Cells[1, 1] = Filepath;
ws.Cells[2, 1] = Period;
ws.Cells[3, 1] = FiscalYear;
//~~> Run the macro ControlMacroAct
xlApp.Run("ControlMacroACT");
//~~> Clean-up: Close the workbook
xlWorkBook.Close(false);
//~~> Quit the Excel Application
xlApp.Quit();
}

Exception thrown while closing Excel

Morning,
I am writing simple windows service that will take excel file from given location, generate xml file and move excel to another folder.
I am using:
Excel = Microsoft.Office.Interop.Excel
My code looks like this:
Excel.Application xlApp = null;
Excel.Workbook xlWorkBook = null;
Excel.Worksheet xlWorkSheet = null;
try
{
xlApp = new Excel.Application();
xlWorkBook = xlApp.Workbooks.Open(file);
xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item("Części");
//doing something with xml and excel
xlApp.DisplayAlerts = false;
xlWorkBook.Close();
xlApp.Quit();
} catch (Exception e) {
this.writeErrorLog(e);
} finally {
// Close the Excel process
if (null != xlWorkSheet)
Marshal.ReleaseComObject(xlWorkSheet);
if (null != xlWorkBook)
Marshal.ReleaseComObject(xlWorkBook);
Marshal.ReleaseComObject(xlApp);
GC.Collect();
}
My problem is that when i run it as normal program it works fine and does everything i need. But when i create service and install it, it creates exceptions every time i upload excel file to this folder. Exception says that program could not gain access to my excel file.
System.Runtime.InteropServices.COMException
I have checked this topic but it didn't help me. Can anyone help me solve this problem?
EDIT: Btw. I am using this tutorial to create service.
EDITv2: The way i take file paths:
string sc_path = #"C:\Projekty\AAPLXML\AppFolders\upload";
string tg_path = #"C:\Projekty\AAPLXML\AppFolders\processed";
if (System.IO.Directory.Exists(sc_path) && System.IO.Directory.Exists(tg_path))
{
List<string> files = System.IO.Directory.GetFiles(sc_path).ToList();
if (files.Count == 0) return;
files.ForEach(f => new XmlGenerator(f).Start());
}

Excel Instance wont close after Interop Operations

I'm building a new Excel workbook in c# by combining the first sheet of a series of different Excel workbooks; subsequently I export the new Workbook to PDF. I made this work, but there is always one Excel instance running by the end of the method.I had the same issue discussed here with a simpler setup and less Excel objects that I could solve with the GC.Collect command. Now, none of this is working.
public void CombineWorkBooks()
{
Microsoft.Office.Interop.Excel.Application xlApp = new Microsoft.Office.Interop.Excel.Application();
xlApp.DisplayAlerts = false;
xlApp.Visible = false;
Workbooks newBooks = null;
Workbook newBook = null;
Sheets newBookWorksheets = null;
Worksheet defaultWorksheet = null;
// Create a new workbook, comes with an empty default worksheet");
newBooks = xlApp.Workbooks;
newBook = newBooks.Add(XlWBATemplate.xlWBATWorksheet);
newBookWorksheets = newBook.Worksheets;
// get the reference for the empty default worksheet
if (newBookWorksheets.Count > 0)
{
defaultWorksheet = newBookWorksheets[1] as Worksheet;
}
// loop through every line in Gridview and get the path' to each Workbook
foreach (GridViewRow row in CertificadosPresion.Rows)
{
string path = row.Cells[0].Text;
string CertName = CertificadosPresion.DataKeys[row.RowIndex].Value.ToString();
Workbook childBook = null;
Sheets childSheets = null;
// Excel of each line in Gridview
childBook = newBooks.Open(path,Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);
childSheets = childBook.Worksheets;
if (childSheets != null)
{
// Build a new Worksheet
Worksheet sheetToCopy = null;
// Only first Worksheet of the Workbook belonging to that line
sheetToCopy = childSheets[1] as Worksheet;
if (sheetToCopy != null)
{
// Assign the Certificate Name to the new Worksheet
sheetToCopy.Name = CertName;
// set PageSetup for the new Worksheet to be copied
sheetToCopy.PageSetup.Zoom = false;
sheetToCopy.PageSetup.FitToPagesWide = 1;
sheetToCopy.PageSetup.FitToPagesTall = 1;
sheetToCopy.PageSetup.PaperSize = Microsoft.Office.Interop.Excel.XlPaperSize.xlPaperA4;
// Copy that new Worksheet to the defaultWorksheet
sheetToCopy.Copy(defaultWorksheet, Type.Missing);
}
System.Runtime.InteropServices.Marshal.ReleaseComObject(sheetToCopy);
childBook.Close(false, Type.Missing, Type.Missing);
}
System.Runtime.InteropServices.Marshal.ReleaseComObject(childSheets);
System.Runtime.InteropServices.Marshal.ReleaseComObject(childBook);
}
//Delete the empty default worksheet
if (defaultWorksheet != null) defaultWorksheet.Delete();
//Export to PDF
newBook.ExportAsFixedFormat(Microsoft.Office.Interop.Excel.XlFixedFormatType.xlTypePDF, #"C:\pdf\" + SALESID.Text + "_CertPres.pdf", 0, false, true);
newBook.Close();
newBooks.Close();
xlApp.DisplayAlerts = true;
DownloadFile(SALESID.Text);
System.Runtime.InteropServices.Marshal.ReleaseComObject(defaultWorksheet);
System.Runtime.InteropServices.Marshal.ReleaseComObject(newBookWorksheets);
System.Runtime.InteropServices.Marshal.ReleaseComObject(newBook);
System.Runtime.InteropServices.Marshal.ReleaseComObject(newBooks);
xlApp.Quit();
System.Runtime.InteropServices.Marshal.ReleaseComObject(xlApp);
GC.Collect();
GC.WaitForPendingFinalizers();
}
protected void DownloadFile(string Salesid)
{
string path = #"c:\\pdf\" + Salesid + "_CertPres.pdf";
byte[] bts = System.IO.File.ReadAllBytes(path);
Response.Clear();
Response.ClearHeaders();
Response.AddHeader("Content-Type", "Application/octet-stream");
Response.AddHeader("Content-Length", bts.Length.ToString());
Response.AddHeader("Content-Disposition", "attachment; filename=" + Salesid + "_CertPres.pdf");
Response.BinaryWrite(bts);
Response.Flush();
Response.End();
}
The problem must have been related to the call of the DownloadFile Method. I eliminated that call, and the Excel process was properly closed. Some of these operations must have kept a reference to one of the COM objects open, so that they could not be closed. By calling "DownloadFile" at the very end after the GarbageCollect the problem is solved. (I'm not quite sure why)

In your method DownloadFile, you call
Response.End()
HttpResponse.End throws an exception (emphasis mine):
To mimic the behavior of the End method in ASP, this method tries to raise a ThreadAbortException exception. If this attempt is successful, the calling thread will be aborted, [...]
This exception aborts your thread. Thus, all your ReleaseComObject, Excel.Quit, GC.Collect stuff is never executed.
The solution: Don't call Response.End. You probably don't need it. If you need it, you might want to consider the alternative mentioned in the documentation instead:
This method is provided only for compatibility with ASP—that is, for compatibility with COM-based Web-programming technology that preceded ASP.NET. If you want to jump ahead to the EndRequest event and send a response to the client, it is usually preferable to call CompleteRequest instead.
[...]
The CompleteRequest method does not raise an exception, and code after the call to the CompleteRequest method might be executed
PS: Using Excel automation from a web application is not officially supported by Microsoft. For future development, you might want to consider using a third-party Excel library instead.

I found that sometimes the only thing that helps is the "sledgehammer method". Killing all running excel instances:
foreach (Process p in Process.GetProcessesByName("EXCEL"))
{
try
{
p.Kill();
p.WaitForExit();
}
catch
{
//Handle exception here
}
}

Looks to me that you have a reference not cleaned up. Probably something like the 'two dot rule' problem - which in my opinion is a silly rule because you can't code anything decent because it's to difficult to keep track of.
You could try Marshal.ReleaseComObject of your COM references but still asking for trouble...
My suggestion would be to try using VSTO to automate Excel. This will clear your references correctly on your behalf.
https://social.msdn.microsoft.com/Forums/vstudio/en-US/a12add6b-99ea-4677-8245-cd667101683e/vsto-and-office-objects-disposing

How can I open the current instance of Excel from my application?

How can I open my Excel worksheet in the current open instance of Microsoft Excel? When I use my code, a new instance of Excel is opened.
private Excel.Application xlApp;
private Excel.Workbook xlWorkBook;
private Excel.Worksheet xlWorkSheet;
xlApp = new Excel.Application();
xlApp.Visible = true;
xlWorkBook = xlApp.Workbooks.Open(textBox1.Text);
xlWorkSheet = (Excel.Worksheet)xlWorkBook.ActiveSheet;

You can do something like the following to get a reference to a running Excel instance (if there is one):
public Excel.Application TryGetExistingExcelApplication()
{
try
{
object o = Marshal.GetActiveObject("Excel.Application");
return (Excel.Application)o;
}
catch (COMException)
{
// Probably there is no existing Excel instance running, return null
return null;
}
}
Once you have a reference to a running instance, you can access it's Workbooks collection.
One caveat: if you try to automate an existing Excel instance, you may get "server busy" exceptions. To avoid this, you can implement IOleMessageFilter error handlers. This article describes how to do it for automating Visual Studio; the technique is identical for automating Excel.