Plain file backup is basically a straight copy job. In the New Task Wizard in BackupChain the option is called “no processing” because no compression, encryption, or deduplication is being used (see link to step-by-step article at bottom).
A great bonus in BackupChain is you can keep more than one copy of each file, if you want. For example, you could configure your plain file backup copy job to keep all revisions of *.doc files, but only one (the latest) copy of all *.vhdx files. These configurations are done in the File Types tab table, see example below; the relevant column is “Number of Backups”:
Step-by-step instructions on how to set up a plain file backup in BackupChain (bottom of article)
and A Quick Intro to BackupChain File Retention Settings (talks about how the column “number of backups” controls the length of each file’s history in the backup folder)
Or, have a look at the User Guide (accessible from the top menu)