A Simple Solution Overlooked?

My database contains documents which are entered randomly (i.e. - not in any particular order). But then, for my reports, I must show these documents in “Document Number” order, once I have gotten them in the order I want (usually by date or other criteria).
In Access 2003, (in query mode) all I had to do was enter the number 1 in the first “document number” field, then number 2 in the second document number field. Then, by pressing and holding the “down arrow” key, this field automatically filled in the document number consecutively from 3 through whatever number of documents I have in my database. Very quick and efficient. I’ve had Access since the very first edition (1996 I think), thus I don’t remember how I was able to get the “Document Number” field to “self-fill” in the query mode, but have been doing this for years.
Now, I cannot get Access 2007 to do this, no matter what I do, thus I am forced to manually enter the number for each document.
Question: How can I get the “Document Number” field to fill-in the series automatically (in query mode) by pressing and holding the ‘down arrow’ key? As I said, the information is entered at random and has to be sorted later by document number, thus I cannot use a Primary Key or AutoNumber for this.