Can I back up single file or specific files through File Backup or NAS Backup?

Yes, Vinchin Backup & Recovery supports wildcard filters function to backup specific files for file backup and NAS backup. 

Wildcard filter function helps you to choose the files you want or not want to backup. It has three options: None, Exclusion and Inclusion. If you choose None, backup files/folders which you have selected won’t use any filter. If you choose Exclusion, backup all files except the ones to be excluded by exclusion filters. If you choose Inclusion, only backup files which will be matched by the inclusion filters.

You can choose either include or exclude files by typing ‘*’ or '？', for example, you can type '*.docx' or '?.docx' to include or exclude the files has filename with .docx to be backup.  Please note that ’*’ can match 0, 1 or multiple characters, '?' can only match 1 character.