My Writer documents, saved as .doc and .docx, are opening as .txt files. They are filled with seemingly random characters. My Calc and pdf files are fine.

Only the writer files are unusable. They are also much larger than I remember.

To get a relevant answer, please, edit (see the gray link below your question, above this comment) your question to cite OS and LO version, how you open the files (double-click, menu open, start center, …), how they were created (are they old or recent?). Generally, give maximum number of technical facts because we aren’t above your shoulder to watch your screen.