You can use Adobe Acrobat or another PDF generating utility and "print" your statements from FMP 6 in PDF format. The resulting PDFs can be stored in containers in FMP 10 if you want.
Have you actually tried converting your files to FMP 10?
Granted, it's not as simple a process as one would like, but if you're willing to put up with the multiple file structure, most of your database files should convert error free. I've converted many 5.5 files, which are even older, and only had to fix a few scripts and just one or two calculated field definitions before my converted files were working identically to my originals. The only external script issue that I ran into was that sometimes the converted scripts didn't bring the correct window to the front and this was very easy to find and correct. The major pain in conversion is merging the files and this isn't necessary in order to get your converted files up and running.
I bow to PhilModJunk about the conversion on a spiritual plane.
But my experience has been that earlier databases are not simplistic or well-designed and the conversion can be a nightmare.
I would exhibit the early ver3 or ver5 multi databases that I designed as an example, but...
Elegance, simplicity, complete understanding leads to the same in conversion.
Am still seeking that enlightenment.
In my limited experience, a problem-free conversion is more of an exception than a rule. However, the suggested process might be even worse: while it's not difficult to create an image of a preview and store it in a container field, getting that image into another file in a newer version is not simple at all. I think your time may be better spent rewriting the entire solution from scratch.
If you haven't actually done so. I'd suggest using a copy of FMP 10 (you can download a free trial version for this purpose) to convert your files, then test and examine them for problems. That'll give you a far better picture than any of our posts as to whether you should convert the files or start over from scratch.