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1) Go to Playstore and install Firefox Browser for Android.
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2) Then install Acrobat Reader.
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3) Then open an invoice > Then click on the share icon > Print as HTML (no internet)
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4) Then choose Firefox to open the html file.
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5) Then under Firefox browser, click on your menu > Tools.
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6) Then click on Save as PDF

To send the PDF to your email:

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1) Open the create pdf > Choose Acrobat Reader.
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2) Then click on the share icon on the top menu
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3) Then choose your email app. It will attach the pdf to your email.