XnView Software

Without checking the file name shown on the top right corner, it is very hard to tell that the file opened is a pdf or picture file. A file might be mis-deleted due to an oversight of the file type. Hopefully, an option of showing a label of pdf or highlighting the file type can be provided.

Thanks.

you can change the color for thumbnails of PDF file

I mean the "View' mode. There is no thumbnails there. For example: