Today I recovered some documents after rebooting system. All were garbage. Tried documents that were not open for a long time; they are all garbage. Do I have a faulty release of LibreOffice Writer?
Did you close down LibreOffice before shutting system down?
Did the operating system crash?
Do you save in native Open Document Format (odf) or in a foreign format like doc?
Is your hard drive failing?
Maybe the OS font cache is damaged?
You have not mentioned what version you have, see Ask/Guide - How to use the Ask site - The Document Foundation Wiki
If you have a file or two among your damaged documents which you are sure to not hold sensitive content (i.e. safe for public disclosure; this is a public place), you could upload that file here (preferably by editing your initial question posting and attach file there).
Alternative if there is a helper who volunteers, and whom you would trust: share file with them in private.
A sample file would enable us to at least identify (and possibly rectify) some causes for this kind of problem.
I’d say unlikely, because you seem to be the only one.
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Even without sharing a file there is something you can test yourself:
Copy one of your “garbage”- files and rename it to something like garbage.zip (You may get a warningvabout changing the extension, but continue, as this is a copy of your file.)
Now try to open the file with a double click (or whatever your OS needs to start a file). If the file is readable you should see abfolder structure, as all LibreOffice-files are also zip-archives, and most OS can open them zoday directly.
When you open this files, is it really LibreOffice opening the files or does some other software open them?
Another point to check may be file-level encryption or not available/synced cloud storage. Worst case may be encryption by some ransomware. As you didn’t gave any details it is only guesswork…