PDF printing only works with android 4.4.4 due to bug I'm working on fixing. Mailing any help is appreciated.

Free old version at https://play.google.com/store/apps/details?id=com.alucardfox.CoolBTTPrinter

Allows printing of text and images with most ESC/POS thermal printers
ESC/POS are not very good at printing images, so there may be gaps if the image is denser than simple outlines.
ESC/POS do not support Unicode, so you cannot print unicode characters, only the most basic ASCII.

This app creates shortcuts to the home screen for quicker use of the printer.
You can also use 'SEND TO'/'SHARE' functionality to send image/pdf/text to the app: Picturepad or Notepad

Notepad activity lets you write/paste text to print directly to the printer in ASCII, using primitive formatting (double width, double height, underline, strikethrough).

Picturepad activity lets you pick a picture from gallery/files to print directly, there is facility to convert the image to solid black/white, using 'contrast sliders' and rescaling.
You can also rotate the image if you so wish by tapping it.

This app is an updated release of "Cool Bluetooth Thermal Printer" (lost my keystore...) with little to no settings, and is specifically designed for "hobby use" of a 5802LD thermal printer.

If there's suggestions, I will include them in the app. So please write suggestions and feature requests, I may include them. If there is any demand, I will add a settings tab to make other printers supported.