Merge Lines In A Text File

I am working with an old line-feed printer text file. There are characters in the first position of each line that tell the printer what to do, i.e. print this line and advance paper, print and do not advance. when processing this text file for conversion to another text file I can't seem to work out the code for merging two lines. For example,

Type: Location: Quantity:
+ 123 London 45000

After processing the line should look like this:
Type: 123 Location: London Quantity: 45000

I understand the concept but have no idea how to actually merge the two lines with code.