If a file is in warning status, and the detection result shows one of the supported codepage, it means the file could be a text file which is saved in certain codepage, but UTFCast is not very sure of the result, so that the file will not be converted, and a warning is generated.
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 that they look like text files. In this case, an erroneous result of codepage detection could happen, and a warning is generated.
UTFCast has a self-test mechanism to know if an erroneous result could be happening, and then shows the notice. In some cases, you may just ignore the warnings because most of the files are actually binary files. In some other cases, you may want to accept the result because the detected codepage is correct. The warnings are shown to get your attention in case of an unnoticed mistake. If you think the detection result is correct and would like the conversion engine to convert the file for you, you can use the Accept result function to convert it, or use Make correction function to specify another codepage with a preview.
Here's the detailed steps: How to get rid of warnings