How can I use the revision history of a file attachment in a formula for another field?

The API Guide contains an appendix describing the file attachment path, and specifically how to access various revisions: https://help.quickbase.com/api-guide/index.html#filemanagement.html

has anyone solved this yet?  I have the same question.  looking at the API guide, it would be nice fi there were a formula for VID like DBID, but that isn't the case

I know you can reference the version # when you are creating a formula field to read the value of the file attachment.

URLRoot() & "up/" & Dbid () & "/a/r" & [Record ID#] & "/e240/v0"

Not sure about pulling the number of revisions.

Maybe consider using a child table as the "Document" storage location, and then you can count the number of child documents, and have all sorts of control of revisions that way.

The version information of a file attachment is only available through the API_DoQuery method with the format structured (ie &fmt=structured) being requested.

<field id="6" field_type="file" base_type="text">    <label>file</label>
  <nowrap>0</nowrap>
  <bold>0</bold>
  <required>0</required>
  <appears_by_default>1</appears_by_default>
  <find_enabled>1</find_enabled>
  <allow_new_choices>0</allow_new_choices>
  <sort_as_given>1</sort_as_given>
  <carrychoices>1</carrychoices>
  <foreignkey>0</foreignkey>
  <unique>0</unique>
  <doesdatacopy>0</doesdatacopy>
  <fieldhelp/>
  <max_versions>3</max_versions>
  <see_versions>1</see_versions>
  <use_new_window>1</use_new_window>
</field>

If you need access to the version information you have to use script or mockup your own versioning system using a child table as Matthew suggested.