Suppose a file is in warning status, and the detection result shows one of the supported codepages. In that case, it means the file could be a text file saved in a certain codepage, but UTFCast is not very sure of the result, so it will not convert the file, and that's why it generates a warning.
Some files are very similar to text files, such as PDF files and ZIP archives of many text files. These files are not in text format, but they contain too much text, so they look like text files. In this case, an erroneous result of codepage detection could happen.
UTFCast has a self-test mechanism to know if an erroneous result could happen and then shows the notice. You may ignore the warnings in some cases because most files are binary files. You may want to accept the result in some other cases because the detected codepage is correct. The warnings are shown to get your attention in case of an unnoticed mistake. Suppose you think the detection result is accurate and would like the conversion engine to convert the file for you. In that case, you can use the 'Accept result' function to allow the conversion or use the 'Make correction' function to specify another codepage with a preview.
Here are the detailed steps: How to get rid of warnings