The PDF Embedder plugin has a translation template file located in the /lang/ folder within the plugin directory. You can use the pdf-embedder.pot to translate the plugin to another language.
You will want to use a program such as POEdit (free) to open the template file (pdf-embedder.pot) and create your translation.
Location of lang folder in plugin heirarchy
You will save your translated file as pdf-embedder-xx_XX.po where xx_XX is the language code for your translation (this corresponds to the language selected in your WordPress installation under Settings > Site Language).
Upload both the PO and compiled MO files back into the /lang/ folder. Both files must be uploaded for the translation to work: the PO file tells the plugin what text strings are translated and the MO file applies the new words.
Flush any caches on your site and reload the page where the PDF has been embedded. The translated text should now appear on the embedded viewer.