I have received a few replies from other forums and just thought I would share one of the responses in case it is helpful for anyone else. It is not what I will be using but someone may find it useful.
COMMENT
Word cannot automatically “number” lines with letters. The Line Numbering feature has no option to change the format of the numbers; and the paragraph numbering feature is exactly that, the sequential numbering of paragraphs rather than lines. (In Word, a paragraph is any length of text that ends with a paragraph mark, what you called a hard return.)
There is a way to fake it. This is best done only after all other editing has been completed, or else you’ll have to go through the whole document to make adjustments.
• Click in the first paragraph of text. Turn on nonprinting characters by clicking the ¶ button on the Home tab so you can see paragraph marks.
• Click Insert > Text Box > Draw Text Box.
• Draw a box in the left margin, from the bottom of the header area to the top of the footer area.
• In the text box, insert nine line breaks (Shift+Enter).
• After the last line break, press Ctrl+F9 to insert a field (it looks like a pair of braces, { } ).
• Between the field braces, type this: SEQ a *Alphabetic
• Press F9 to update the field, which will now appear as the letter A.
• Copy the set of nine line breaks, the field, and the paragraph mark at the end.
• Put the cursor between the A and the paragraph mark and paste three times. You now see four As, one at each 10th line.
• Press Ctrl+A to select everything in the text box, and press F9 to update all the fields. You should now have A through D on the first page.
• If necessary, move the text box up or down to align the letters with the correct lines of text.
• Click the edge of the text box and copy it to the clipboard.
• Paste a copy of the text box into the first paragraph of each page, position it as needed, select its contents, and press F9 to update its fields.
You may need to add or delete some line breaks to match up the letters with the correct lines.
(Note to other readers: Don’t suggest anchoring the text box in a header or footer. SEQ fields don’t work anywhere but in the main text story.)
Hope this helps.