Why do I not get the checkout option for a pdf type document when clicking on the document link in the SharePoint workflow task?

We are trying to use workflows to review and edit pdf files in sharepoint 2010. We are having a couple of issues and am hoping someone has the answer.....

1)  When myself and coworkers click on the pdf document in the library, we get the check out option as expected.  However when we click on the document link in a workflow task (on the sharepoint site), the pdf opens as a temporary file and we do not get the check out option.  Why does this happen????? 

2)  The same thing happens when we click on the document link in the workflow task email;   HOWEVER,  one of our co-workers does get the check out option when clicking on the link in the email task.  Why would she get the checkout option using the email and not when clicking on the link in the task list on the sharepoint site ????  We have compared our internet settings and adobe settings to ours and found no differences.

We are using Sharepoint 2010, Windows 7, IE8, Adobe Reader X or XI.  Some of us have Adobe Pro X and have the same issues.