The third-party output of the various eID infrastructures is not standardized, which means that there can be several different resulting files. Looking at some of the Scandinavian eIDs; Danish NemID uses XMLDSIG as the output format, Norwegian BankID uses SEID SDO and Swedish BankID uses PKCS#7.
Information about the different eID infrastructures can be found here: ID Methods
In order to view, interpret and validate the signed documents, the third-party output format typically requires a solution such as Signicat Viewer. Furthermore, the storage of the combined proof of signature (which includes certificate status at the time of signature as well as transaction events) calls for an archive solution such as Signicat Archive, which is tailor-made for handling digitally signed documents.