As a temporary workaround, you can script a button that uses the Export Field Contents script step to download the container contents. Or instruct users to right click and select the export field contents script step.
I am seeing this issue in (mac) Chrome 36.0.1985.125
In (mac) Safari 7.0.5 (9537.77.4) I see the container contents as expected and am able to interact, but the scroll bars are missing per this known issue:
In IE10 (windows) I only see a link to the PDF.
Upon further testing, it seems like it does work in Chrome (my primary browser on mac). Just takes a while to preview depending on circumstances that I haven't completely defined.
I think maybe if the PDF doesn't have an embedded preview it might take longer, also depending on how it was generated.
Clients need a PDF plugin installed.
For Windows that normally means to install Adobe Reader.
That's not necessarily true though. Chrome has it's own PDF extension built-in.
FileMaker Inc's KnowledgeBase answer # 5812 indicates the following limitations for WebDirect PDF content:
Publishing Container field data to the web using FileMaker WebDirect
FileMaker WebDirect was introduced in FileMaker Server 13.
Container data can be embedded inside the solution itself or stored externally when using FileMaker WebDirect. FileMaker WebDirect does not support container data that is linked by reference.
By default, container fields are optimized for static content. Therefore web users cannot play video or audio files or open PDF files. If a container field is set for static content, web users see either a static graphic or a link to the data in the container field. Container fields optimized for interactive content allow web users to play media files and tointeract with PDF files.
Data stored in interactive container fields use progressive downloading over an unencrypted connection, even when SSL is enabled. Progressive download must be enabled in the FileMaker Server Admin Console to access interactivecontainer data via encrypted connections.
So, there are several settings to check, both for the content storage method, field settings, and even Server 13 settings.