It was always a challange to order custom flag from any flag maker or any sign shops. The file formats we are used to see in everyday life like .jpeg files are useless for flag production. Flag printers need special file formats to print laser sharp flags or banners.
In general, they are called vector file formats. Vector files are made of lines, not pixels. Regardsless of how many times you enlarge a vector file, the sharpness stays same unlike the files made from pixels.