I am creating a library by building source of wkhtmltopdf which is having a LGPLv3 license. Is it legal to change the file names of wkhtmltopdf source used in my library ? My library will be integrated to a commercial application. If it is OK to change can you share some website or resource which describes that file name change of LGPLv3 source code is legit.
Of course it is legal to make changes to an open source programme or library - that's the point.
In the case of a strong copyleft license like the GPL you are, however, required to provide the sources to your customers of the changed versions which you distribute - and it's necessary to indicate that you made changes to the version (thus you have to give credit to the original contributors as by the license requirements, but you also may not wrongfully attribute the modified work (only) to other people).
In some cases where the actual name is trademark registered it may be required to change the name you distribute the programme or library under, if you want / need to distribute modified versions.
In the particular case of an LGPL - licensed C/C++ - library you will need to allow replacing the libary on the provided product. For dynamically-linked libraries this is no problem: the user just needs to be able to rebuild the library. For statically-linked libraries this is usually done by providing the object files to your binary so the users can re-link the binary with a modified library. In both cases you might simply want to publish the sources of your library in a repository with clearly-tagged versions used for distribution.