Validate if a file looks like an RTF. The test should be seen as a minimal requirement; If failed, the file is highly likely that the file is invalid, while passed, there is still possibility that the file does not follw the rule of RTF files.
looks_rtf(con, n = 1000)Logical.
A connection object or string of file name
Integer that specifies the length of contents to be tested. If smaller than 10, forced to 10.