How to fix
Run Adobe Acrobat Reader 8.x
Edit menu, Preferences
Multimedia Trust icon, Trusted Documents radio button, [x] Allow Multimedia Operations
Multimedia Trust icon, Other Documents radio button, [x] Allow Multimedia Operations
Trust Manager icon, [x] Allow Opening of Non-PDF File Attachments with External Applications
...and reversed them for safety when done.
Why use safer settings?
If these non-default settings stop things like SARS e-filing from working, why apply them?
Acrobat Reader is an exploitable surface that has often been patched to "fix" it, and for which unpatched vulnerabilities often exist. Commercial enterprises have already exploited the by-design safety gap, e.g. by having .PDF documents "call home" when they are read, so that their usage can be tracked.