Huge format wars such as VHS vs. Beta or Blu Ray vs. HD DVD get all attention, but some people appreciate that +R(W) and --R(W) designations on DVD media show two formats that at war. It is not likely one ever win out over other as hardware makers are building combo drives that easily read and write to either, but they are separate technologies, so compatibility problems do arise. There is no direct conversion from one format to other, but you can easily obtain information on +R over to a --R disk.
• Run copy with DVD burning software first. Though, many programs show error. Copy function makes .iso, or picture of disk contents and structure, which is particular to media format, but various programs work in various methods, so give try first. Just copy data from +R disk and burn it to --R disk. If that doesn’t work, there are tools claim to be able copy among formats, but they are costly.
• Rip DVD +R to hard disk. The + and -- designations relate to media and drive, not to the actual data on the disk. The data remains the same as it was before it was burned, so ripping it just regains raw data to hard drive.
• Purchase few blank --R media and burn data right back to disk. This is tricky part if you have older DVD drive on PC that doesn’t handle both formats. If that is case, you must move data, on stick or portable hard drive, to PC that has combo drive. This must not hard as each PC built as about 2006 that comes ready with a DVD drive can hold + and -- formats without trouble. Also, new --R disk must be friendly on separate players as +R disk was.