The speaker is a office worker, and the title, "Paper pusher," sets that up right away. The poem turns on a single image: all morning the speaker feels like "thin paper," flimsy and easily used up. By afternoon the feeling shifts from being paper to simply doing work, which is not "a book to be."
That last line is the sting. A book is something whole, lasting, and meaningful, and the speaker suggests that a day of paperwork never adds up to anything like that. Sheets get shuffled and handled, but nothing gets made. The speaker seems to feel thin, replaceable, and unfinished.
The opening "Lord" reads like a weary sigh, or half a prayer, and gives the poem a tired, plaintive tone. It's brief and dry, with a little gallows humor. The mood is one of quiet frustration, the sense of a day slipping away without leaving anything solid behind.