Merge legal and letter sized pdf docs into one pdf file

When I attempt to merge a singe page legal size pdf document into a letter size multi-page pdf document, the legal document is truncated into letter size.

As a result, I am have lost some of the top portion of the legal size document.

How can I reslove this problem?


The blog says pdfforge is working on a tool for this:

Meanwhile, there is an open source tool that I like, called pdfsam: