外来文件 meaning in English

documents of external origin

Since i m dealing with a foreign file format , i want to eliminate the risk of encountering any control characters along the way
既然在处理外来文件格式，我想消除在中途遇到任何控制字符的风险。
Excuse me , which contains in the external document ? should the relative law rules belongs to the exeternal document ? should i take a single folder to collect the law rules
请问一下,外来文件包括哪些呢?是不是相关的法律法规也属于外来文件?那是不是单独放一个文件夹作为法律法规的收集