Yes, converting supplier invoices into other formats is generally legally compliant as long as the integrity and authenticity of the invoice data are maintained throughout the process.
Under the EU VAT Directive, the authenticity of origin, the integrity of the content, and the legibility of an invoice must be ensured until the end of the storage period. Several countries, including Sweden and Germany, also require an e-invoice to be kept in the format it was received in, so keep the original file alongside the converted version. See How long must e-invoices be stored?.
Conversion does not change what the invoice must contain. For the mandatory content and the extra rules for e-invoices, see What must an invoice contain? VAT invoice requirements explained.
Qvalia stores all original invoices for you for as long as you are a Qvalia customer. The legal retention period can be longer than the customer relationship, so export your invoices before an agreement ends.