Read ebook and pdf stored on ub device with android 6+

[Xwang]

Hi to all,
my old android 4.4 tablet does not work any more and I've a newer one with Lineageos 16 (android 9).
Up to now I used to use "Document Viewer: PDF, DjVu,... " (https://play.google.com/store/apps/d...ysecure.viewer) to read my e-book and pdf which are stored in an USB pen drive attached to the tablet using an OTG cable.
Android 6 and following have a different USB management and I'm not able to use that program any more because it does not have access to the USB mounting point.
Is there any android app which permit to read e-book and pdf files from an USB OTG pen drive?

[AnotherCat]

There are likely a number of apps that will also do so, however I use Pocketbook Reader app for reading ebooks and that reads books from OTG connected USB storage, including pdf and epub (Android 9 OS on OTG capable devices). Pocketbook is available from the Google Play Store free, no ads.

I suspect that the popular Moon+ Reader app will too, although I sometimes use it I haven't tried it with OTG. Again, in the Play Store, free with ads, and paid version.

For a PDF only reading app Xodo reads off OTG storage for me (available in the Play Store, free, no ads).

On OTG capable devices I would expect that most File Managers will copy from OTG storage to the device's internal storage (certainly the ones I have used do).

[Xwang]

I've tried Pocketbook but it have access only to the /storage folder and my tablet does not create the /storage/xxxxx when I mount the USB pen drive, it only creates the /mnt/media_rw/xxxxx one.
On my Motorola Moto G5 Pocketbook works perfectly because the /storage/xxxxx is created.
Moreover in Pocketbook I haven't found a way to move files as I was ablr to do with Document Viewer which on the Moto G5 seems to be able to only read files but not to write to the USB.

[AnotherCat]

Pocketbook on my phone does not see books on OTG USB storage (although I have never tried hard to see if there is some way) whereas my tablets do.

However, on my phone if I navigate to the book on the USB using a file manager or via Settings>Storage and launch the book Pocketbook is offered to read it and will work. BUT Pocketbook copies the book to its own folder in the device's internal storage so persists after the OTG USB is disconnected.

I just now tested Moon+ Reader Pro on my phone and it does not seem to see the OTG USB either. My phone uses Google's own near stock Android One version of Android 9 whereas my tablets on which readers do see the USB books are Samsung so have Samsung's own Android 9 version on them.

So it may be that the ability for Pocketbook, etc to see books on the USB depends on the OEM's version of Android or maybe on the build of the reading app (the phone or tablet build, for example).

[Xwang]

At the end it seems I've resolved installing a different custom rom which creates the reflection of the mount point in /storage.
A lot of apps now are able to see the folders in the USB, but the older ones suffer when I try to move or delete files.