PiPO Ultra-U8 - Manual (Page 17)

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Tap or the menu button to check the sub-menus. You can set the
font size, Go to Page jump; check your bookmarks, set the auto flip time,
etc.
6.6 Sign function
Tap the ―sign‖ icon to open this.
You can make notes and sign your signature on PDF, Picture file.
Just tap to choose the PDF file from your tablets, make
sure you have those files in your tablets.
If you want to make note or want to sign on pictures, Please tap
. You may edit the documents and pictures as you want.