E-invoices are structured, machine-readable data files which are not suitable for reading in the normal way. To display e-invoices in a human-readable format, data visualisation software is required. There are numerous suppliers of such software on the market. And KoSIT (the Coordination Office for IT Standards) provides a free development component for visualisation (Link: https://www.xoev.de/xrechnung-16828#GÜ). If using an ERP system, you should not need additional visualisation software, as most ordinary ERP systems provide visualisation.