Per / As per
UsagePer and as per can both mean according to or in accordance with. In concise operational writing, per is enough; as per is valid but more formal and often heavier.
Per
Use when
You mean according to or in accordance with a stated instruction, list, plan or source and want the shorter business or operational construction.
Example
“Let's shift them per the flight manifest.”
As per
Use when
You mean the same thing and deliberately want the more formal or traditional business or legal construction.
Example
“Let's shift them as per the flight manifest.”
Quick check
adding as only to make routine instructions sound more formal, treating per as ungrammatical when it means according to, repeated as per phrasing that makes operational writing needlessly heavy
Usage note
Do not label as per ungrammatical. Merriam-Webster records both forms in this sense and notes that as per is common in business and legal prose but can sound ponderous. For a broad audience, according to or in accordance with may be clearer than either.