You can use PDF Reader Pro to merge your PDF documents into a new PDF file.
1. Enter the reading page and tap Editor on the toolbar.
2. Tap Merge to combine multiple PDF files into a new PDF document, and you can also borrow individual pages from other PDF files to merge.
3. Tap + Add Files to add documents that you want to combine together.
4. Set the Page Range and click Merge to start merging.
Or you can find Merge in Quick Tools on Home to quickly complete the PDF merging task.