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There is no direct way to get a PCB file from a scanned bitmap. There are some programs that produce input for PCB programs from bitmaps, but they produce a pattern of fills. The fills will give you a huge PCB file that cannot easily be edited.
However, you can convert raster scan files, such as bitmap, to vector files, such as DXF or DWG. There are a bunch of raster-to-vector converters you can find using a search engine such as G00GLE
You can then use a gerber program such as C@M350 or GERBT00L to read the DXF or DWG file and save it out as a gerber file. You can edit the gerber file in the gerber editor, or you can import it into a PCB program such as PR0TEL. You will still need to manually enter such info as hole sizes, and padstacks.
Bottom line - it is a lot of work. Usually, it is easier to just layout the board in the PCB editor from scratch.