PDF/A for long-term archiving

PDF/A is a format for archiving digital documents on a long-term basis, and was standardized by the International Organization for Standardization (ISO) as a subset of the Portable Document Format (PDF). The standard defines how the features of the underlying PDF versions must be used in relation to long-term archiving. There are compulsory and non-permitted components.
Source: Wikipedia

The use of widespread, standardized components increases the chance that interfaces, data formats, and other parameters will also be supported further into the future. However, there are cases where archived data becomes more difficult or impossible to use subsequently. Unlike many other data formats, Adobe’s PDF format ensures that the pages always appear in the same way, regardless of the output device.

With PDF, there are no nasty surprises for the user. Even so, PDF in the current widely available versions is only a suitable format for long-term archiving due to its structure and technical environment. In order to use it for this purpose, various restrictions as well as additions need to be applied to the conventional PDF, which is why PDF/A Standard (ISO 19005-1:2005) was created. It is based on PDF version 1.4 (corresponding to Adobe Acrobat 5), and defines the additions and restrictions needed to ensure that a PDF is suitable for archiving.

PDF/A-3

The PDF/A-3 specification was published on October 17, 2012. The containers are a significant development compared to PDF/A-2: Any file type can be embedded within PDF/A-3. In this way, for example, source data with which it was produced can be added to a PDF/A-3 document. The standard regulates the suitability of embedded files for archiving where they are not themselves PDF/A-compatible (source: Wikipedia).

ZUGFeRD

PDF/A-3 opens possibilities for electronic invoicing. With this standard, a file and machine-readable data can be stored in XML-format, as well as PDF versions of the invoice suitable for archiving. In June 2014, the ZUGFeRD standard was published, which is based on the PDF/A-3 format (source: Wikipedia).