troutrunner.....there is no super quick fix here
1. have the .PDF file printed or plotted out by a 3rd party...it will probably be on an A4 sheet
2. take the sheet home and then measure the hull length between perpendiculars as per the print
3. determine your desired length of vessel and then record the % increase in hull length between perpendiculars you require
4. as others have suggested, take the same .PDF file to a Copy Shop....do not use the word scale ......but the % increase you require
5. remember the paper plan is two dimensional.....length & breadth....
6. explain to the copy shop person you need the plan enlarged by the same XYZ % in
both length and breadth
You would be amazed at how different people interpret non specific requests

..... Derek