An open file format is the source file in which your design was originally created by the graphic designer. It comes in CDR (coreldraw), AI (Illustrator) or PSD (Photoshop) format.
The resolution for any artwork should be above 300 dpi (dots per inches). It is a standard requirement used accross industry. To understand if your file is of a good resolution or not, refer to this detailed article here. Why is the resolution ...
300 dpi (dots per inch) is the resolution of the output PDF file. Print resolution is measured in dots per inch (or “DPI”) which means the number of dots of ink per inch that a printer deposits on a piece of paper. So, 300 DPI means that a printer ...
You can upload artworks in PDF, CDR, AI or PSD formats to get the quality print output. Avoid uploading low resolution PNG, PDF or JPEG files to print. Read more about low resolution artwork here.