Dec 08, 2015 · I created a VSTO Excel AddIn to insert information from a webservice in a excel xlsx file. At least I implemented a autostart function. If I open a excel with text “autostart” in cell A1 with doubleclick, the addin receive informations, insert the informations to excel - this works fine.

So the whole excel worksheet could be kept in memory. Excel file format. After a little bit of searching on the net, I decided on the Excel 2.1 Workbook format (description of the format found here). Even though this format is old, it can be imported by Excel or by other programs and it seemed suitable for our simple needs.