BAK files are generally just renamed backup copies of the original file, so if your file was PDF, you can simply rename it back and open using PDF Reader.
If that is not possible, the BAK file is not a PDF and there is no way how to convert it. One last option would be to use some file analyzer software to determine what kind of .bak file it is and whenever it may be even exported as PDF document.
Updated: February 2, 2017
This conversion entry was verified by us and conversion was flagged as wrong or not possible.
Usually this happens when the conversion would try to convert different types of data between each other, such as audio to image, or it is not possible because incompatibility between programs, caused by closed file formats, very limited support etc.
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