A4 Trifold is the perfect size. It is compatible with various products on the market (such as Mayayayu payment, Sale, Orbic Promise, Net de wage, PCA, Knee, Solimato, Invoice, Sales slips, etc.). Compatible with inkjet printers, digital printers, and perforated printing machines. Please note that the laser printer may have some wrinkles than the model. A4-format tri-fold and 3-section storage window layout to ensure the address is visible. The envelopes are double sided tape on the lid for a smooth seal after sealing the paper. It is also environmentally friendly and can be recycled, without sorting after use. We created an ecology and economy concept. (Can be recycled, without separating the windows) [Privacy protection that prevents contents from see-through] [Comes with a tape for convenient sealing] Weve got all your needs.