Excel – VBA Compatibility between different Office Versions

You can use a library called ExcelLibrary. It's a free, open source library posted on Google Code:

ExcelLibrary

This looks to be a port of the PHP ExcelWriter that you mentioned above. It will not write to the new .xlsx format yet, but they are working on adding that functionality in.

It's very simple, small and easy to use. Plus it has a DataSetHelper that lets you use DataSets and DataTables to easily work with Excel data.

ExcelLibrary seems to still only work for the older Excel format (.xls files), but may be adding support in the future for newer 2007/2010 formats.

You can also use EPPlus, which works only for Excel 2007/2010 format files (.xlsx files). There's also NPOI which works with both.

There are a few known bugs with each library as noted in the comments. In all, EPPlus seems to be the best choice as time goes on. It seems to be more actively updated and documented as well.

Also, as noted by @АртёмЦарионов below, EPPlus has support for Pivot Tables and ExcelLibrary may have some support (Pivot table issue in ExcelLibrary)

Here are a couple links for quick reference:
ExcelLibrary - GNU Lesser GPL
EPPlus - GNU (LGPL) - No longer maintained
EPPlus 5 - Polyform Noncommercial - Starting May 2020
NPOI - Apache License

Here some example code for ExcelLibrary:

Here is an example taking data from a database and creating a workbook from it. Note that the ExcelLibrary code is the single line at the bottom:

//Create the data set and table
DataSet ds = new DataSet("New_DataSet");
DataTable dt = new DataTable("New_DataTable");

//Set the locale for each
ds.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;
dt.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;

//Open a DB connection (in this example with OleDB)
OleDbConnection con = new OleDbConnection(dbConnectionString);
con.Open();

//Create a query and fill the data table with the data from the DB
string sql = "SELECT Whatever FROM MyDBTable;";
OleDbCommand cmd = new OleDbCommand(sql, con);
OleDbDataAdapter adptr = new OleDbDataAdapter();

adptr.SelectCommand = cmd;
adptr.Fill(dt);
con.Close();

//Add the table to the data set
ds.Tables.Add(dt);

//Here's the easy part. Create the Excel worksheet from the data set
ExcelLibrary.DataSetHelper.CreateWorkbook("MyExcelFile.xls", ds);

Creating the Excel file is as easy as that. You can also manually create Excel files, but the above functionality is what really impressed me.

You can try this direct VBA approach which doesn't require HEX editing. It will work for any files (*.xls, *.xlsm, *.xlam ...).

Tested and works on:

Excel 2007
Excel 2010
Excel 2013 - 32 bit version
Excel 2016 - 32 bit version

Looking for 64 bit version? See this answer

How it works

I will try my best to explain how it works - please excuse my English.

1. The VBE will call a system function to create the password dialog box.
2. If user enters the right password and click OK, this function returns 1. If user enters the wrong password or click Cancel, this function returns 0.
3. After the dialog box is closed, the VBE checks the returned value of the system function
4. if this value is 1, the VBE will "think" that the password is right, hence the locked VBA project will be opened.
5. The code below swaps the memory of the original function used to display the password dialog with a user defined function that will always return 1 when being called.

Using the code

Please backup your files first!

1. Open the file(s) that contain your locked VBA Projects

2. Create a new xlsm file and store this code in Module1

   code credited to Siwtom (nick name), a Vietnamese developer

   Option Explicit
   
   Private Const PAGE_EXECUTE_READWRITE = &H40
   
   Private Declare Sub MoveMemory Lib "kernel32" Alias "RtlMoveMemory" _
           (Destination As Long, Source As Long, ByVal Length As Long)
   
   Private Declare Function VirtualProtect Lib "kernel32" (lpAddress As Long, _
           ByVal dwSize As Long, ByVal flNewProtect As Long, lpflOldProtect As Long) As Long
   
   Private Declare Function GetModuleHandleA Lib "kernel32" (ByVal lpModuleName As String) As Long
   
   Private Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Long, _
           ByVal lpProcName As String) As Long
   
   Private Declare Function DialogBoxParam Lib "user32" Alias "DialogBoxParamA" (ByVal hInstance As Long, _
           ByVal pTemplateName As Long, ByVal hWndParent As Long, _
           ByVal lpDialogFunc As Long, ByVal dwInitParam As Long) As Integer
   
   Dim HookBytes(0 To 5) As Byte
   Dim OriginBytes(0 To 5) As Byte
   Dim pFunc As Long
   Dim Flag As Boolean
   
   Private Function GetPtr(ByVal Value As Long) As Long
       GetPtr = Value
   End Function
   
   Public Sub RecoverBytes()
       If Flag Then MoveMemory ByVal pFunc, ByVal VarPtr(OriginBytes(0)), 6
   End Sub
   
   Public Function Hook() As Boolean
       Dim TmpBytes(0 To 5) As Byte
       Dim p As Long
       Dim OriginProtect As Long
   
       Hook = False
   
       pFunc = GetProcAddress(GetModuleHandleA("user32.dll"), "DialogBoxParamA")
   
   
       If VirtualProtect(ByVal pFunc, 6, PAGE_EXECUTE_READWRITE, OriginProtect) <> 0 Then
   
           MoveMemory ByVal VarPtr(TmpBytes(0)), ByVal pFunc, 6
           If TmpBytes(0) <> &H68 Then
   
               MoveMemory ByVal VarPtr(OriginBytes(0)), ByVal pFunc, 6
   
               p = GetPtr(AddressOf MyDialogBoxParam)
   
               HookBytes(0) = &H68
               MoveMemory ByVal VarPtr(HookBytes(1)), ByVal VarPtr(p), 4
               HookBytes(5) = &HC3
   
               MoveMemory ByVal pFunc, ByVal VarPtr(HookBytes(0)), 6
               Flag = True
               Hook = True
           End If
       End If
   End Function
   
   Private Function MyDialogBoxParam(ByVal hInstance As Long, _
           ByVal pTemplateName As Long, ByVal hWndParent As Long, _
           ByVal lpDialogFunc As Long, ByVal dwInitParam As Long) As Integer
       If pTemplateName = 4070 Then
           MyDialogBoxParam = 1
       Else
           RecoverBytes
           MyDialogBoxParam = DialogBoxParam(hInstance, pTemplateName, _
                              hWndParent, lpDialogFunc, dwInitParam)
           Hook
       End If
   End Function
   

3. Paste this code under the above code in Module1 and run it

   Sub unprotected()
       If Hook Then
           MsgBox "VBA Project is unprotected!", vbInformation, "*****"
       End If
   End Sub
   

4. Come back to your VBA Projects and enjoy.