I think it is more a directory thing.
First you need root rights ( so sudo gainroot or root) is required in advance) But it looks like you did.
So depending on above command, you are located in /home/user or /root. Your deb file is inside /home/user/MyDocs (or maybe /home/user/MyDocs/.documents).
What you need is change to that directory (cd /home/user/MyDocs) or give full path (dpkg -i /home/user/MyDocs/1armel.deb).
AND autocompletion is always recommended.