Hi,
Sorry, we don't support creating pdf portfolios. What we do support is having attachments to a pdf file, which is the basics portfolios are created with. Basically, Acrobat 8 added pdf packages, which are a "cover sheet" pdf file with attachments and some extra metadata for the attached files.
Acrobat 9 added portfolios, which are a pdf package + actionscript/flash actions to do extra stuff + some other extra stuff like icons for the attached files.
We could update the attachments to be pdf packages, but update the packages to portfolios is kind of out of the scope of FlexCel, since another file format (flash/swf) comes into picture.
What you can do right now is to create the "cover sheet" pdf by exporting some coverhseet excel file (or by creating the pdf with the API), and then attaching other pdfs/xlsx files you create to this cover sheet. But this is not really a portfolio: a portfolio would be that + more metadata and actionscript to make it more interactive.
Thank you for the answer.