There is no method of eliminating use of CID Identity-H encoding when creating PDF files. Such encoding is perfectly valid per the PDF specification. It is often used when large character sets are used or non-ASCII characters are referenced. There are absolutely no settings in any Adobe preferences or options to avoid this encoding. Furthermore, any software that is attempting to interpret text within a PDF file should be able to deal with such encoding. It seems like this “Bing Mailroom” software is making very poor assumptions about the PDF files that it will need to interpret. You should contact that company's tech support to get a fix from them for their software.
You did mention your transition from Windows 7 to Windows 10. One of the major changes that most users are not aware of is that in the transition from Windows 7 to Windows 8.x to Windows 10, the system fonts within Windows (such as Arial, Times New Roman, etc.) grew dramatically in size in terms of the numbers of glyphs defined in those fonts (to support more languages, special symbolic characters, etc.). When encountering such fonts, some if not most PDF generators will use CID Identity-H encoding. The only thing you might try is use of other fonts that are much more restricted in the number of glyphs they support, probably meaning that you may need to license fonts other than the Windows system fonts.
- Dov