What is the symbol called 10

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Allowed characters

- recommended: alphanumeric characters of the English alphabet: a-z, A-Z, 0-9. The special characters hyphen (-) and Underscore (_) be used.

- allowed but not recommended: Umlauts and Spaces. Windows 10 can handle these characters, but servers often cannot, which can cause errors.

Characters that shouldn't be used

- not allowed: \ / : * ? " < > | . Saving a file with a file name that contains one of these special characters is not possible in Windows 10.

- allowed but not recommended: all other special characters - except for the hyphen (-) and underscore (_). Using these special characters can cause errors.

Large and lower case

Windows makes no distinction between uppercase and lowercase letters when naming files. It is therefore not possible to save two files within a folder that only differ in this property (e.g. Test.pdf and test.pdf). 

length

The length of the file name should be as short as possible and as long as necessary.

One of the reasons for this is that the path within the drive is limited to 256 characters in Windows. This length can be achieved quickly with long file (and folder) names. Errors can occur if the length of 256 characters is exceeded. Further information on this topic can be found in the FAQ "Opening files with too long filenames".