LibreOffice can read, edit, and save documents in several formats. It is not necessary to convert files from those formats to the OpenDocument format used by LibreOffice to use those files. However, if you want to convert the files, you can do so. To convert several documents, such as when first switching to LibreOffice, do the following:
Select File › Wizards › Document Converter.
Choose the file format from which to convert.
Click Next.
Specify where LibreOffice should look for templates and documents to convert and in which directory the converted files should be placed.
Documents retrieved from a Windows partition are usually in a subdirectory of /windows.
Make sure that all other settings are correct, then click Next.
Review the summary of the actions to perform, then start the conversion by clicking Convert.
The amount of time needed for the conversion depends on the number of files and their complexity. For most documents, conversion does not take long.
When everything is done, close the Wizard.