I have now installed HPLIP 3.14.3 and the situation has improved significantly.
Following installation, the default page size hadn't changed to letter - it was still A4.
The test print is now correct.
I can now set the printer (Officejet 6700) to be single-sided (previously it always reverted to double-sided).
I can now print my test pdf file without loosing anything. However, to do that I have to print it single sided. Most files now print correctly, but I have found that to print some double sided files correctly, I have to print the first side single-sided, load the paper back into the printer and then print the second side.
I have now installed HPLIP 3.14.3 and the situation has improved significantly.
Following installation, the default page size hadn't changed to letter - it was still A4.
The test print is now correct.
I can now set the printer (Officejet 6700) to be single-sided (previously it always reverted to double-sided).
I can now print my test pdf file without loosing anything. However, to do that I have to print it single sided. Most files now print correctly, but I have found that to print some double sided files correctly, I have to print the first side single-sided, load the paper back into the printer and then print the second side.