Try to find the example blocks "a3", "screw" or "t-part" from the "Library Browser".
You'll see that they are simply DXF files stored in the default library folder.
Where the default library folder is, depends on your operating system. Normally you'll find it in the program folder. There look for the sub folder "resources/library". Or use your file browsers search function to find "a3.dxf".
You can either save the library files using LibreCAD's "Save as..." function or copy them with your preferred file manager.
You can also add your own library folder in the "Paths" tab in "Application Preferences", then the default libraries and your own are listed in the "Library Browser". You have to restart LibreCAD to apply the new library path.
Thanks to dellus
Thank you for your explanation
The problem is that I can not select all the blocks before exporting them, so I need one file per block type.
And even in this case, I can not copy a drawing part of an open application to another (also open) with a copy / paste
Do you have a solution?
Thank you for your answer
Given that each block is a separate .dxf file they will have to be saved individually. For your open file transfer issue, and given you will have separate files, you could consider duplicating your original file by block name and removing all but the appropriate block from each of them. Regardless of approach it is likely to be a repetitive process.