Any file in the source tree can have the '.ad' suffix appended. Autodist will process any file that has the suffix when the source tree is prepared for configuration and compilation (see Preparing source tree). If the files have distdef conditionals the Autodist will process them. The files will have the '.ad' suffix removed.
Basic rule is, if you need to process some file when preparing the source tree for configuration and compilation, add '.ad' suffix to it. Distdefs (see Distdefines) can be used in any file in source tree but without '.ad' suffix Autodist will not process those files during preparation. They will be processed when creating the distribution package. If you need processed files during configuration or compilation then they need to have '.ad' suffix.
Note that, the distdef format used in these files must be the non-source format, even if the file is source file. This is because the distdefs are processed during source tree preparation, and the source file will have all distdefs removed when it is compiled.