You can specify a page number offset in an APA file. You can enter simple addition + and subtraction - expressions in page assignment instructions in APA files.
Math expressions are valid with or without spaces.
Note: Geometry assignments do not support addition and subtraction.

In the Page Assignments view, page offsets look like this:

In the Raw APA File view, the same instructions are:
ASSIGN= "Page.p[#PgPosition].pdf" "Pageset1" [#PgPosition] 1
ASSIGN= "Page.p[#PgPosition].pdf" "Pageset1" [#PgPosition] 1
ASSIGN= "Page.p[#PgPosition].pdf" "Pageset1" [#PgPosition] + 50 + 30 1

Example 1

This example includes all the page assignment statements for a book that consists of seven files. The page position is calculated using the page number from the page name plus the number of pages in each of the preceding files.

The 10 pages from the 1_frontcovers file are assigned to page positions one to 10.
The 38 pages from the 2_intro file are assigned to page positions 11 to 48.
The 516 pages from the 3_chpt_1 file are assigned to page positions 49 to 565.
The 8 pages from the 4_chpt_2 file are assigned to page positions 566 to 574.
The 30 pages from the 5_chpt_3 file are assigned to page positions 575 to 605.
The 8 pages from the 6_chpt_4 file are assigned to page positions 606 to 614.
The pages from the 7_appendix file are assigned to page positions from 616 on.

Example 2

This example includes page assignments for a book that includes the starting page number in the page names. For example, Page_28_56.p1.pdf has a starting page number of 28.
The page position can be calculated by adding the starting page number (for example 01 or 28) and the page number (for example 1 from P1, 2 from P2, 3 from P3, and so on), then subtracting 1. For example, for page name Page_28_56.p3.pdf, the page position would be 28 + 3 - 1 = 30.
Refined filenames are as follows:
Page_01_27.p1.pdf
Page_01_27.p2.pdf
Page_01_27.p3.pdf
... Page_01_27.p27.pdf
Page_28_56.p1.pdf
Page_28_56.p2.pdf
Page_28_56.p3.pdf
... Page_28_56.p56.pdf

In the Raw APA File view the instructions to assign the pages would be:
ASSIGN= [$][#Start][$].p[#PgPosition].pdf "" [#Start]+[#PgPosition] -1 1*

One way to add the instruction in the APA Editor is to type the ASSIGN= statement in the Raw APA File view. If you do that the wild cards will be correctly named. Alternatively, you can start entering it in the Page Assignments view and make any required additions or changes in the Raw APA File view.
In the Page Assignments view, the instruction will look like:

If you typed the ASSIGN statement in the Raw APA File view, the  wild cards have the names Start and PgPosition. You can check the wild card names by moving the cursor over the wild card icons.
When the APA instruction is executed, the resulting page assignments will be:
Page_01_27.p1.pdf is assigned to page position 1.
Page_01_27.p2.pdf is assigned to page position 2.
Page_01_27.p3.pdf is assigned to page position 3.
... Page_01_27.p27.pdf is assigned to page position 27.
Page_28_56.p1.pdf is assigned to page position 28 + 1 - 1 = 28.
Page_28_56.p1.pdf is assigned to page position 28 + 2 - 1 = 29.
Page_28_56.p1.pdf is assigned to page position 28 + 3 - 1 = 30.
... Page_28_56.p56.pdf is assigned to page position 28 + 56 -1 = 83.

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