There is good news in that the images for M1368 are now available on the Catalog for free, thanks to a collaborative effort by NARA and Fold3. You can go to the link for the Catalog (catalog.archives.gov), search for the Catalog ID, and it should be the first link that pops up.
In this instance, the "Petitions and Records of Naturalization, 1790 to 1991" series from the District of Massachusetts can be found here: https://catalog.archives.gov/id/595176
However, you can also search the Catalog for the name you are looking for, and if the images are on the Catalog, it might come up right away. Here are the arrival papers for Christian H. Johannessen: https://catalog.archives.gov/id/59261710
Of course, if you want a copy or scan of the original document, you can contact the National Archives at Boston by calling 866-406-2379 or emailing firstname.lastname@example.org. Copies and scans of naturalization documents are $10.00.
National Archives at Atlanta