Why does my "PDF Download" arrive as a file named "(2)" without an extension and opens only as text character stream?

First line appears as:
%PDF-1.5
%âãÏÓ
4 0 obj
<</Filter/FlateDecode/Length 10>>stream
xœ+ä  î |
endstream
endobj
5 0 obj
<</Filter/FlateDecode/Length 661>>stream
xœm•MoÛ0†ïþ:n@¢ˆõul Vl@»C¯Aâ^“´s»
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