I have found that .png images with a transparent background will show correctly in Excel when inserted on a worksheet with a background colour, but if the same worksheet is converted to PDF the image background becomes opaque. I have also tried gif format with the same result.
The attached zip file contains a Visual Studio 2008 Web Application to demonstrate the problem. The zip file also contains a file named "AsposeOutput.png" which shows screen captures of Excel 2007, Excel's Print Preview and Adobe Reader X's rendering of the corresponding pdf file (with only the png's inserted - I captured this before trying gifs)
You will need to create the Library directory and add Aspose.Cells.dll to it before attempting to run the demo. I tried using the dlls posted to
<A href="</A><BR>but they seem to be missing several things, in particular the WorkbookSave(Response...) methods. Are these updates "net3.5_ClientProfile" versions? It would be helpful if you would put a note in that thread to say so!
Please let me know if any further information is required.
Regards - Andrew