EUDC fonts are designed to draw end-user-defined (nonstandard) characters. The glyphs for EUDC-characters can be created with EUDC Editors. The interval for these characters depends on code page. i-net Clear Reports retrieves information for the characters in unicode private use area (E000 - F8FF). Therefore your custom characters must lie in this interval.
Then your EUDC font must be embedded i.e. must be installed in the directory for embedded fonts.
Prior to i-net Clear Reports 9.1, the EUDC characters could be shown only in pdf export and only if EUDC font was set for the text containing custom characters. Since 9.1 you can set a not-EUDC font for some mixed text containing both EUDC and standard characters. In addition to pdf export, the EUDC characters can be shown in java viewer. The font for the mixed text must be embedded as well. (This requirement could be removed in future versions).