German law distinguishes between statutory and contractual written form requirements. If the written form is required by statute, the document must be authenticated by the issuer personally by means of his signature or by a handwritten mark certified by a notary. In the case of a contract, both parties must sign on the same document. The written form can be substituted by the electronic form and by notarisation. Where the written form requirement is merely a contractual stipulation, it is sufficient for the declaration of intent to be transmitted by means of telecommunication and, in the case of a contract, by exchange of letters.
The concept of a document/deed (Urkunde) is not consistent in German law. A document in terms of criminal law is not consistent with a document in terms of civil or procedural law, and even within the civil and procedural law the term is not consistent.
You can find a collection of sample contracts on the websites listed below: https://www.frankfurt-main.ihk.de/recht/mustervertrag/
You also can find a checklist on the website https://www.verbraucherzentrale.de/englisch-neu. There are written in English. For example, there is a list who gives important information before signing a contract.