Attribute error: 'NoneType' object has no attribute 'GetLayer' geoPDF

Question

I have written some code to export projection information from geoPDF’s. For some reason on some of the files I get the following error and other are fine.

    AttributeError: 'NoneType' object has no attribute 'GetLayer'

As I understand the above error it means that the proj variable is empty. When I check the files with GDALINFO it clearly shows the projection information

My Code

    fileName = 'filename'
    filePath = 'path/to/file/'

    driver = ogr.GetDriverByName('PDF')
    dataset = driver.Open(filePath + fileName +'.pdf')

    # from Layer
    layer = dataset.GetLayer()
    spatialRef = layer.GetSpatialRef()
    # from Geometry
    feature = layer.GetNextFeature()
    geom = feature.GetGeometryRef()
    spatialRef = geom.GetSpatialReference()

    spatialRef.MorphToESRI()
    file = open(filePath + fileName +'.prj', 'w')
    file.write(spatialRef.ExportToWkt())
    file.close()

    print (neatline_wkt)
    print (spatialRef)

Some PDF files raise the following error but others don't. For example this file has projection information embedded as per below - https://usfs-public.box.com/shared/static/26rhbxx7oqxdtw5efxi5asd894cwbmwb.pdf but causes an error.

    gdalinfo CA_Plumas_National_Forest_Greenville_MVUM.pdf
    Driver: PDF/Geospatial PDF
    Files: CA_Plumas_National_Forest_Greenville_MVUM.pdf
    Size is 5250, 3412
    Coordinate System is:
    PROJCS["NAD_1983_UTM_Zone_10N",
        GEOGCS["GCS_North_American_1983",
            DATUM["North_American_Datum_1983",
                SPHEROID["GRS_1980",6378137.0,298.257222101]],
    PRIMEM["Greenwich",0.0],
    UNIT["Degree",0.0174532925199433]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["False_Easting",500000.0],
    PARAMETER["False_Northing",0.0],
    PARAMETER["Central_Meridian",-123.0],
    PARAMETER["Scale_Factor",0.9996],
    PARAMETER["Latitude_Of_Origin",0.0],
    UNIT["Meter",1.0]]
    GeoTransform =
     620218.9230522923, 14.39324062623421, -4.455847902786653e-06
     4470454.925909669, 0.0001940513634986329, -14.39592969090605
   Metadata:
     CREATION_DATE=D:20190529162113-08
     CREATOR=Esri ArcMap 10.5.1.7333
     NEATLINE=POLYGON ((649617.508764131 4422834.69664129,649617.465150077 
     4468987.38965106,694136.387837796 4468987.60928566,694136.315653489 
     4422835.67742383,649617.508764131 4422834.69664129))
     Corner Coordinates:
     Upper Left  (  620218.923, 4470454.926) (121d35' 1.84"W, 40d22'33.65"N)
     Lower Left  (  620218.908, 4421336.014) (121d35'34.82"W, 39d56' 0.99"N)
     Upper Right (  695783.436, 4470455.945) (120d41'39.34"W, 40d21'42.13"N)
     Lower Right (  695783.421, 4421337.033) (120d42'33.00"W, 39d55'10.27"N)
     Center      (  658001.172, 4445895.979) (121d 8'42.09"W, 40d 8'54.83"N)
     Band 1 Block=5250x1 Type=Byte, ColorInterp=Red
     Band 2 Block=5250x1 Type=Byte, ColorInterp=Green
     Band 3 Block=5250x1 Type=Byte, ColorInterp=Blue

Similar file - https://usfs-public.box.com/shared/static/jv6cf5tp30smo4t1kei9i807xjbnxrmm.pdf has no issues and can create projection file.

Any clues on how to resolve?