Q:

How can I access excel properties like creation date with C# and Excel interop

I have to extract the creation date of an excel file using C# and Microsoft.Office.Interop.Excel.Worksheet. 
I will get the properties with 
object props = myworkbook.CustomDocumentProperties;

Now I am not sure how to get the creation date from this object. 

A:

The Creation Date can be found in the BuiltinDocumentProperties property which returns a Microsoft.Office.Core.DocumentProperties collection that represents all the built-in document properties for the workbook. 
Microsoft.Office.Core.DocumentProperties properties;

properties = (Microsoft.Office.Core.DocumentProperties)Globals.ThisWorkbook.BuiltinDocumentProperties; 

Microsoft.Office.Core.DocumentProperty prop;
prop = properties["Creation Date"]; 

See How to: Read from and write to document properties for more information. 

