Most characters, including special characters and copyright symbols, are allowed in filenames, metadata, collections, and categories. Most languages can also be used. There are, however, a few restrictions, which are listed below. 

Avoid using these:

• < > : “ / \ | ? * , + % # ( ) [ ] { } - _

• A space at the beginning or end
• A space before the file extension
• A period at the beginning or end
• A filename that ends with .appl
• These DOS-reserved filenames: AUX, CLOCK$, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, CON, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, LPT9, NUL, PRN
  Certain Latin, Asian, Arabic, and other characters, and some advanced mathematical symbols, also cannot be used.