How to install the latest reader on iPad with 10.3.1?

Two possibilities:

(1) When you “open” the bank statement, what are you actually using to view the PDF file? On iOS, unfortunately, an application such as Adobe Acrobat Reader cannot own a file type, such as PDF. If you open an e-mail with an attachment, either the e-mail client will use its own PDF renderer or it will use the iOS PDF display. You have to “copy” the PDF file to Adobe Acrobat Reader for it to be opened in that application.

(2) Assuming that in fact you are attempting to actually read the PDF file in Adobe Acrobat Reader, this would be an indication that the file is a special type of PDF file, one that uses what is known as XFA forms (typically produced by the Adobe LiveCycle Designer and server products. These PDF files cannot be opened by the Adobe Acrobat Reader on mobile devices. One way to test this hypothesis is to open the PDF file with either Reader or Acrobat on either MacOS or Windows. If it opens there but not in Adobe Acrobat Reader for mobile devices, this is indeed the reason; it is an XFA forms-based PDF file.

          - Dov