How long the contents of personnel files must be stored varies, depending on various factors like company policy or country's laws. In some cases, its up to 30 years after an employee leaves the company, for example, when an attempt is made to claim a pension. In Germany, if the personnel files contain tax-relevant documents, they must be kept for six years. Can companies just keep paper records? Well of course but what about the risks like receipts on thermal paper are no longer readable after such a long time. In addition, purely paper-based storage requires additional space on top of a risk that the documents will be destroyed by fire or water. In addition, the Federal Data Protection Act stipulates that sensitive files must be stored in such a way that only personnel department employees have access to them. So it makes sense to store personnel files digitally.
Dietrich von Seggern, Managing Director of callas software, compares the four formats TIFF, JPEG, PDF and PDF/A and explains why PDF/A is the best choice for digital personnel records: https://www.callassoftware.com/en/blog/digital-personnel-records-for-eternity