Hi Miguel,
I'm sorry for the delayed response.
Actually, Aspose.Pdf currently supports FileStream and ImageStream only. it doesn't support System.Web.HttpInputStream. This issue has been logged as PDFNET-6989; Neverthless, you can use memory stream as a work around. That is, you can convert input stream into memory stream before using it with Aspose.Pdf.
Here is the sample to give you an idea:
//declare a base stream instance
Stream stream;
//create a byte array
byte[] bytearr = new byte[FileUpload1.PostedFile.ContentLength];
//initialize base stream to be read
stream = FileUpload1.FileContent;
//read stream data into byte array
stream.Read(bytearr,0,FileUpload1.PostedFile.ContentLength);
//create a MemoryStream object and fill write data from byte array
MemoryStream inputStream = new MemoryStream(bytearr);
//assign this inputStream to the ImageStream of Aspose.Pdf
img.ImageInfo.ImageStream = inputStream;
//Now, save to the destination stream
MemoryStream destStream = new MemoryStream();
pdfDoc.Save(destStream);
Above code sample worked for all types of image files.
If you find any issue I would be happy to help you out.
Regards.