If you want to split a document into multiple ones by every n pages in Word, you can configure the Split Document feature as follows:

1. Please open your Word document you will split, and click Kutools Plus > Split.

2. In the Split Document dialog, please configure as follows:
(1) Choose Every n pages from the Split by drop down list;
(2) In the Every n pages box, please type a number as you need. For example, you want to save every 4 pages as separate document, you can type 4 into this box;
(3) In the Save to box, please select the destination folder you will save the new documents into;
(4) In the Document Prefix box, type prefix for each document name as you need.

3. Click the OK button.

Now each n pages (each 4 pages in my case) is saved a separated document.

In some cases, you may want to split a Word document by custom page ranges, says save page 1-2, page 3-10, page 11-15, and page 16 as 4 individual documents separately. Here, you can apply the Split Document feature to solve this problem.

1. Please open your Word document you will split, and click Kutools Plus > Split.

2. In the Split Document dialog, please configure as follows:
(1) Choose Custom from the Split by drop down list;
(2) In the Page box, please type the custom page ranges as you need, and separate these page ranges with comma. In my case, I will type 1-2,3-10,11-15,16 in the Page box;
(3) In the Save to box, please select the destination folder you will save the new documents into;
(4) In the Document Prefix box, type prefix for each document name as you need.

3. Click the OK button.

Now your Word document is split by the custom page ranges at once.