That's not due to the size of the file, it's due to the way the fonts are encoded in that particular PDF file.
To validate if that's the case: open the original PDF in Acrobat Reader, then try to select and copy some text to the clipboard, then pasting it into a text editor: you'll probably discover the copied text is garbled as well.
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Technical Product Manager
I don't want to achieve immortality through my work; I want to achieve immortality through not dying - Woody Allen