It seems that both .ovd and .b27 files are or were in the past used by a program called Ovation. As such, this program is probably your best bet in handling these two file types or converting one to another. Sadly, without Ovation you won't be able to work with any of these documents.
Convert Ovation 1 document file to Ovation Pro for RISC OS document file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert ovd to b27 on Windows
A desktop publishing program for Windows
Convert from ovd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.