AFAIK there is no standard tool in SAP to convert XLS (Microsoft propr. format) to itab you can look for the Abap2Xls project to read XLSX (actually zipped directory of some XML files)
There are tools (like ALSM_EXCEL_TO_INTERNAL_TABLE or Office Integration) which use OLE2 to execute Excel on your PC and paste data back to Abap and itab. But you must copy file to the PC, execute the FM will open an Excel session, so no background task is possible.
Could you consider copy those documents to your network where some Excel triggered task could convert those to csv, xml or other format that SAP would be able to read.
Regards,
Raymond
PS: Łukasz has already answered; it is not because his answer doesn’t solve your problem as you expected that it’s a wrong answer.