Quick, easy and dirty you can add the -E flag in Project->Build options->Compiler settings->other compiler options
If you hit compile now, the generated object file (with the file ending .o in PROJECT_FOLDER/obj/BUILD_TARGET_NAME/SOURCE_FILE_NAME.o) will contain the preprocessed source. You can open it with any text editor you like. Linking will fail obviously. To compile the program again you have to remove the -E flag and make a rebuild: Build->Rebuild