Files lock

[CCPIP]

Hi all - I have problems securing my Word / Excel etc. files on my Synology Nas - I've enabled Webdav and i use Netdrive to access files from outside, this works perfectly, but unfortunately, 2 users can edit, for an example, a word document simultaneously. According Synology then it should be possible to lock the files so it is not possible that 2 users can open the file simultaneously, I do not now if it's me who have not set up users correctly on the NAS, or whether there are errors in NAS/webdav software. Someone who has tried it? and that there may be missing a checkbox or