Introduction: the article discusses the main issues of activities of the investigator while working with documents on the basis of criminal procedure legislation and using forensic knowledge on the study of documents. Materials and methods: some of rules of criminal procedure legislation, regulating certain concepts of procedural and other documents, scientific publications of researchers as well as materials of judicial and investigative practice on the topic under study were research materials. When writing the article, we used normative logical, formal legal and other methods. Results: the article analyzes the concept of a document and distinguishes the difference between a procedural document and other documents. The forensic activity of the investigator with documents is demonstrated and the author’s position to address the issues identified is given. Summary and conclusion: conclusions about the need to define the concepts “document”, “procedural document” and “other documents” and provision for them in Article 5 of the Code of Criminal Procedure are substantiated, and this, in turn, implies the need to improve the existing methods and methods of working with documents as sources of forensically significant information. The authors conclude that new approaches to define the concept of “document”, as well as forms and methods of working with documents are necessary.