Ability to view document prior to submitting it

Yes you can do that in Appian with a!submitUploadedFiles(). If you pass the documentId to documentViewerField directly, it will not render the document.

a!localVariables(
  local!document,
  local!showPreview: false,
  {
    a!fileUploadField(
    target: FOLDER
    value: local!document,
    saveInto: local!document
  ),
  a!richTextDisplayField(
    showWhen: a!isNotNullOrEmpty(local!document),
    value: a!richTextItem(
      text: "Preview Document",
      link: a!dynamicLink(
        saveInto: a!submitUploadedFiles(
          onSuccess: a!save(
            local!showPreview,
            true
          )
        )
      )
    )
  ),
  a!documentViewerField(
    height: "TALL",
    showWhen: local!showPreview = true,
    document: local!document
  )
  }
)

Thanks for sharing this, let me ask how could I do If in the current interface I'm allowing the user to upload multiple documents one after the other.

I'm using a grid to allow the user to add multiple, basically every row of the grid can be a new uploaded document.

Because what I'm seeing is that the viewer component is not available to be used in the grid, is this correct? 

a!fileUploadField(
                  label: "Attach Document(s)" & fv!index,
                  target: cons!DOCUMENTS,
                  maxSelections: 1,
                  value: fv!item.document,
                  saveInto: {
                    fv!item.Document,
                    a!save(
                      ri!Document,
                      a!forEach(
                        items: local!documents,
                        expression: {
                          documenttypekey: fv!item.documenttypekey,
                          title: fv!item.title,
                          document: fv!item.document,
                          uploadedby: fv!item.uploadedby,
                          uploadeddate: fv!item.uploadeddate,
                         
                         
                        }
                      )
                    ),
                    
                  },
                  required: true(),
                  buttonStyle: "STANDARD"
                )

thanks in advance!

Thanks for sharing this, let me ask how could I do If in the current interface I'm allowing the user to upload multiple documents one after the other.

I'm using a grid to allow the user to add multiple, basically every row of the grid can be a new uploaded document.

Because what I'm seeing is that the viewer component is not available to be used in the grid, is this correct? 

a!fileUploadField(
                  label: "Attach Document(s)" & fv!index,
                  target: cons!DOCUMENTS,
                  maxSelections: 1,
                  value: fv!item.document,
                  saveInto: {
                    fv!item.Document,
                    a!save(
                      ri!Document,
                      a!forEach(
                        items: local!documents,
                        expression: {
                          documenttypekey: fv!item.documenttypekey,
                          title: fv!item.title,
                          document: fv!item.document,
                          uploadedby: fv!item.uploadedby,
                          uploadeddate: fv!item.uploadeddate,
                         
                         
                        }
                      )
                    ),
                    
                  },
                  required: true(),
                  buttonStyle: "STANDARD"
                )

thanks in advance!