Trimming a door without pain - as instructed to me by my joiner.....

1. Mark amount to trim off door. Then carefully (using a new stanley blade) score a line along the top surface (this prevents inevitable "rip" marks from using circular saw).
2. Use masking tape and lay 3 strips across door where circular saw will move (saves scuff marking door when cutting).
3. Use a cheap 110v Skil saw or similar, (£50 or thereabouts) but buy a decent saw blade to fit - always check blade before cutting to ensure it is sharp.
4. Cut using circular saw.
5. Only use a plane if less than 2mm to trim. Then mark trim lines around whole door (all 4 sides) with pencil marks to ensure planing is square.

Insurance - when you get your traders liability insurance, add "builder/building trades" skill - additional cost is just a few quid. However this covers you for "general building skills" like fitting doors. Some liability insurance does not like insuring woodworking tool use ... because they can cause so much serious injury! So if you ain't conifident - swallow your pride and hire a joiner.

With a Festool:
Put two small pencil marks at each end of the bottom of the door
Place guide on marks
Set saw to depth of door plus 8mm
Cut
You may have to finish with fine sandpaper