Yes. Currently users can open a total of 40 documents a month. All three of our editors (Presentations, Sheets, and Writer Documents) count towards the free usage limit. Any time you open a document (either a new blank document or an existing document) it will count towards the total usage. For example, if you open the same document 5 separate times, then it will count as 5 document sessions.
As you approach the 40 documents opened in a month, we will send you a quick reminder so that you know you are getting close to your limit of free document sessions.