It is important to find the right person in the organisation. Typically this will be a Sales Manager. If there is difficulty locating a person, make it known that you are approaching them about a request and need to quickly locate the right person to ensure they are included.
An organisation may decide they are not willing to respond. Sometimes they believe they have little chance of success, and the effort involved - which is usually substantial - is not warranted. Thank them for their efforts and move on to the next company.
In order to give everyone an equal chance, you may need a number of days to make phone contact with all the companies before forwarding everyone the document. Allow two or three days to make contact.
It may be suggested that rather than just receive written responses, the vendor makes a personal presentation. It is better to have studied the response before meeting the people involved. You will be better placed to ask relevant questions. Inform the vendors that the ones who make it through this stage will be asked to undertake a demonstration and presentation at the next phase.