Can I add the line number to my repeated table in the PDF?

Sure you can!
In the following example we will draw 50 accounts and display them in a Dynamic PDF. The items will be showcased inside a Table, and each table row will be numbered. 

Let's start:
1- Create a new blank form
- Drag a Section element and make it bigger
- Drag 2 textboxes inside the section. Call one "Account" and the other "Phone.
2- Configure the Salesforce Get integration
- Press on "Set Get" button
- Select the "Account" object
- Turn on the "Execute on load" checkbox
- Choose "All" in the "" radio button and set a limit of 50.
- Map the form fields to the Salesforce fields
Account --> Account Name
Phone --> Account Phone
3- Create a Dynamic PDF with table for repeated items
- Press on the "Edit" icon of the default PDF
- Use the toggle above to swirch to "Dynamic mode".
- Insert a table (3 columnsx 2 rows)
- Use the first row as table header:
in first column type text: Line #
in second column type text: Account name
in third column type text: Account phone
- Now insert the form fields into the second row of the table:
in first column insert -> Section.line
in second column insert ->  Account
in third column insert ->  Phone
- Save the form and
4- Test form:
- Publish form as URL
- Wait for rows to load in the repeated section
- Press on "Submit".
you will then see a preview of your PDF with 50 lines and the line number in each row.