we arent all master joiners,cabinet makers on here we are ceramic tilers, and on a tilers forum the question was asked the best way to do it, nothing wrong with using a manual hand plane to remove the wood but for small amounts like 4/5mm its very hard to remove with a hand saw. no doubt you will have to use a plane or sander to make the cut true. me personally if there less than 5mm i use an electric planer, more than that i use my rip saw then finished off with the planer. i have used manual hand saw on the new moulded doors as they are easy to cut. often enough we dont charge for these little extras for trimming doors etc so why should we make life hard for our selves. use power tools for easy ness, get job done as easy and as quick as we can. just remember doors these days are quite exspensive ranging upto £150/£200 an internal door, if you break it, you replace it.