I would use the Shell command to open the PDF.
The following opens a PDF on my system in MS Edge.

Shell """C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe"" ""G:\Documents\'NCIS'_ What Are Gibbs' Rules_.pdf"""

Follow Hyperlink

I personally find the WebBrowser very practical for displaying PDF files directly in the form.

I teach in the tutoring sector and save worksheets in my database, for example, which I tag with keywords, class levels etc. so that I can select them for my lessons as required.

In addition to this information, which is displayed in subforms, there is also a large WebBrowser in the form that offers a preview before the PDF file is opened in Acrobat Reader (or printed directly).

See also: Edge Browser

The PDF is saved in the database in attachment field not in a folder on the hard drive. How can I retrieve the PDF from the database and then view it in the attachment field in access form or should I use the Acrobat active x control.

I'd stay away from saving things in the Attachment field, it bloats the db and they are difficult to work with, instead follow the idea in Images

Access Email Seminar
Code Vault: Lesson 28: Extract Attachment

I made a different version of Richard’s “Document Index” and combined the ideas of “Images & Hyperlinks”.

Works well for me, can screen shot if you think it would work for you.

Document Index
Access Open Programs Seminar
Hyperlinks