A friend of mine created 18 very simple Word files on his old computer (Windows ME with Office XP). These files were pasted on a usb pen drive, then on the Ubuntu partition of my computer and finally landed on the Windows NTFS partition of my (dual-boot) machine (Windows XP SP3 with Office 2007).
Before opening the files I right-clicked the folder to have the files checked by Avast. There is no virus, but Avast says that it have just scanned 123 files! In fact in the folder there are only 18 Word files: I can’t see any other file (the option to see hidden and system files is enabled). If I check a single doc file, Avast say it have just scanned 6 or 7 files.
One word file (I think it has .docx file extension in your case) is just a zip archive which contains the data in different parts in form of .xml documents. So, one .DOCX file contains several compressed files - and they’re unpacked & scanned. That’s why avast scans more files than just one.