Your post title of "Multivalued field" is misleading. You don't have that, you have single values in each field, some repeated because there are multiple files for a partNumber. A multi-value field looks like this (the separators don't have to be commas).
1,2,3,4
5,6,7
0,8,2,5
Yes you can have partNumber as a PK field if you do as suggested, BUT why do you want the values arranged in columns? That is a spreadsheet approach. Access is not a spreadsheet application; db data is meant to be displayed in rows when multiple records are involved. Unless of course, you are performing aggregate functions over groupings.
You can try a Crosstab query when you get your data normalized as suggested, but you will likely encounter issues with respect to trying to control the number of columns that are output. If the current data set limits the number of filenames to 2, that is all the columns you'll get - not the 3 or 4 you had the previous time.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.