I have installed a lot of fonts before, but this time things are really different. I have downloaded some True Type Font (ttf) fonts. Then paste them in the directory

usr/share/fonts

after that I've restarted LibreOffice writer but don't find them in the font list. No better result with PC rebooting.

Then again paste them in the directory

usr/share/fonts/truetype

and again restarted LibreOffice writer, but still they aren't on the font list.

I've tried in another way. Opened the fonts with font viewer and click on the "install" but the result is same. No improvement at all.

Latest

I've just found that those specific fonts are installed on my system, they present on gedit font list,but not in the LibreOffice font list. So, may be the problem is with LibreOffice.

Very surprising and irritating issue indeed.