"feel free to" is usually used when you have something they want, not the other way round. You possibily mean "Please context me when you have the document ready." - You are waiting for the document, and you want to be contacted when it's ready. We don't normally use "feel free to" for that.
"Please feel free to contact me if you should require further information." - You are offering something; it's up to them whether they want to contact you or not. It would not concern you if they did not contact you. (If it would concern you, don't use "feel free to". Feeling free to do something implies being free not to do it too.)
Feel free to ask follow-up questions if necessary!
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