I have similar problem but i thinking that this is thing very particularity of Excel, then, i have two solutions:
Firts, mark the pivottables for that updating when open file excel, for example: right click on pivot table, then, "Options of Pivot table", then, section "Data", then, mark checkbox "Update when on open file"
Second, create one macro for that update all sheets with pivot table, for example:
Dim Hoja As Worksheet
Dim TD As PivotTable
'
'read each sheet of file
For Each Hoja In ActiveWorkbook.Sheets
'read each pivot table of each sheet
For Each TD In Hoja.PivotTables
'update pivot tble
TD.RefreshTable
Next TD
Next Hoja